Se eu encontrar um erro no relatório, vou corrigi-lo na mesma hora.

Because se + a future possibility usually takes the future subjunctive in Portuguese.

So in this sentence:

• Se eu encontrar = If I find / If I happen to find

This is different from:

• eu encontro = I find / I do find / I usually find

A very common pattern in Portuguese is:

• Se eu tiver tempo, vou ligar.
• Se ele chegar cedo, saímos.
• Se nós pudermos, ajudamos.

So encontrar here is not the regular present tense. It is the future subjunctive form of encontrar.

For many regular verbs, the future subjunctive looks the same as the personal infinitive and often also looks like the dictionary form in the eu and ele/ela/você persons.

For encontrar, the future subjunctive is:

• se eu encontrar
• se você/ele/ela encontrar
• se nós encontrarmos
• se vocês/eles encontrarem

So in this sentence, encontrar is the correct form for eu in the future subjunctive.

That is simply a grammar difference between the two languages.

English uses the present form after if for many future conditions:

• If I find an error, I'll fix it.

Portuguese usually uses the future subjunctive in this kind of sentence:

• Se eu encontrar um erro, vou corrigi-lo.

So even though the English verb looks like a present tense, Portuguese marks this idea more explicitly with a special form.

Both are possible, but vou + infinitive is extremely common in Brazilian Portuguese and sounds natural in everyday speech.

So these are both correct:

• vou corrigi-lo
• corrigirei-o or more naturally corrigi-lo-ei in very formal/literary style

In real Brazilian Portuguese, speakers strongly prefer:

• vou corrigir
• vou corrigi-lo
• or even vou corrigir ele in casual speech, though this last one is less formal according to traditional grammar

So vou corrigi-lo is a very natural, standard way to say it.

-lo means it, referring back to um erro.

Since erro is a masculine singular noun, the direct object pronoun is:

• o = it / him (masculine singular)

When attached after the verb, o becomes lo in this case:

• corrigir + o → corrigi-lo

So:

• vou corrigi-lo = I’m going to correct it

Here, it = the error.

This happens because of how certain object pronouns attach to verbs in standard Portuguese.

When a verb ends in -r, -s, or -z, and you attach o, a, os, as, that final consonant drops, and the pronoun changes:

• o / a / os / as → lo / la / los / las

So:

• corrigir + o → corrigi-lo
• fazer + o → fazê-lo
• encontrar + a → encontrá-la

That is why you do not get corrigir-o.

Because in standard written Portuguese, when an object pronoun is attached to the end of a verb, it is normally linked with a hyphen.

Examples:

• ajudá-lo
• vê-la
• corrigi-lo

This is called ênclise: the pronoun comes after the verb.

In Brazil, everyday spoken Portuguese often avoids this kind of structure, but in careful writing and standard grammar, corrigi-lo is correct and very common.

In everyday Brazilian speech, yes, many people do say that kind of thing:

• Vou corrigir ele

But according to traditional standard grammar, for a direct object, the preferred form is:

• Vou corrigi-lo

So the difference is roughly:

• corrigi-lo = more standard/formal/written
• corrigir ele = very common in speech, more colloquial

For learners, it is useful to recognize both, but corrigi-lo is the safer choice in formal Portuguese.

Because erro is a masculine singular noun.

So:

• um erro = an error
• o erro = the error
• corrigi-lo = correct it / literally correct the-it

If the noun were feminine, the pronoun would change:

• uma falha
• vou corrigi-la

So the pronoun agrees with the gender and number of the noun it replaces.

No is a contraction of:

• em + o = no

So:

• no relatório = in the report

This kind of contraction is very common in Portuguese:

• em + a = na
• em + os = nos
• em + as = nas

Examples:

• no carro = in the car
• na sala = in the room
• nos documentos = in the documents

Portuguese uses definite articles more often than English.

So where English says:

• in the report

Portuguese naturally says:

• no relatório

Without the article, em relatório would sound unnatural here.

In many contexts, Portuguese prefers:

• no trabalho
• na reunião
• no texto
• no relatório

This is something English speakers often just need to get used to.

It means something like:

• right away
• immediately
• on the spot
• at that very moment

Literally, it is at the same hour/time, but in normal usage it often means without delay.

So:

• vou corrigi-lo na mesma hora

means the speaker will correct the error immediately after noticing it.

It is normal and natural, but it is a bit more literal than some other everyday expressions.

Other common ways to express a similar idea are:

• imediatamente
• na hora
• logo
• assim que eu perceber (depending on context)

In Brazilian Portuguese:

• na mesma hora sounds perfectly understandable and natural
• na hora is also very common in speech

The comma separates the conditional clause from the main clause.

• Se eu encontrar um erro no relatório, = condition
• vou corrigi-lo na mesma hora. = result

This is standard punctuation in Portuguese, just as in English:

• If I find an error in the report, I'll correct it right away.

Sometimes Portuguese allows the subject pronoun to be omitted, but here eu helps make the sentence clear and complete.

You will often hear omitted subjects in Portuguese because the verb form already shows the person:

• Se eu encontrar...
• Se encontrar... can sometimes appear in certain contexts, but it may sound less explicit or a bit more ambiguous depending on the sentence

For learners, Se eu encontrar... is the best choice.

Yes, but the structure changes.

You can say:

• Se eu encontrar um erro...
• Caso eu encontre um erro...

Both mean something like if I find an error, but:

• se eu encontrar uses the future subjunctive
• caso eu encontre uses the present subjunctive

Both are correct. Caso can sound a little more formal or more explicitly hypothetical.

The written accent in relatório shows the stressed syllable:

• re-la-TÓ-ri-o

The ó is stressed, which is why the accent is written.

Very roughly for an English speaker in Brazilian Portuguese, it sounds like:

• heh-lah-TOH-ree-oh
  with a tapped/flapped Portuguese r between vowels

The accent mark is important because it tells you where the stress goes and how the vowel sounds.

Very roughly:

• cor-ri-GI-lo

The stress stays on gi because it comes from corrigir.

In careful speech, the attached pronoun is clearly pronounced, so you hear the final lo as part of the same unit:

• corrigi-lo

A rough approximation for an English speaker might be:

• koh-hee-ZHEE-loo or koh-rree-ZHEE-loo, depending on accent

The exact sound of r and g/j varies by region, but the key point is that -lo is attached directly to the verb.

Yes. It is grammatical, clear, and natural, especially in a neutral or somewhat careful register.

A Brazilian speaker might also say more casually:

• Se eu encontrar um erro no relatório, vou corrigir na hora.
• Se eu achar um erro no relatório, vou corrigir na hora.
• Se eu encontrar algum erro no relatório, vou corrigi-lo na hora.

But your original sentence is completely good Portuguese.