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

Because after se meaning if, Portuguese normally uses the present subjunctive when talking about a real possibility in the future.

So:

• Se eu encontrar... = If I find...
• vou corrigi-lo = I’ll correct it / I’m going to correct it

For the verb encontrar, the eu form of the present subjunctive is encontrar, which happens to look exactly like the infinitive. That is why it can seem strange at first.

A quick comparison:

• Se eu encontrar um erro... = future possibility
• Se eu encontro um erro... is not the standard choice here
• Se eu encontrarei... is not used after se

That’s true: Portuguese often does drop subject pronouns. But here eu helps make the subject clear.

The form encontrar could refer to:

• eu
• você
• ele/ela

So if you said only Se encontrar um erro..., it could sound ambiguous without context.

Including eu makes it clear that the meaning is if I find an error.

No is a contraction of:

• em
  • o = no

So:

• no relatório = in the report

This kind of contraction is extremely common in Portuguese.

Some related examples:

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

That’s also why you have na mesma hora later in the sentence:
na = em + a.

Um erro means an error / any error — something nonspecific.

That fits this sentence because the speaker is not talking about one particular known error. They mean: if they happen to find an error of some kind, they will fix it.

Compare:

• um erro = an error, any error
• o erro = the error, a specific one already known in the conversation

In Brazilian Portuguese, ir + infinitive is a very common way to talk about the future.

So:

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

This is often more natural in everyday Brazilian Portuguese than the simple future.

A simple future version would be possible:

• corrigirei = I will correct

But that sounds more formal or written.
So vou corrigi-lo is very natural in Brazilian Portuguese.

-lo is a direct object pronoun meaning it.

Here it refers to um erro, because:

• erro is masculine
• erro is singular

So:

• corrigi-lo = correct it

Grammatically, both erro and relatório are masculine singular nouns, but in meaning it is clearly the error that is being corrected, not the report itself.

When certain object pronouns are attached to an infinitive, Portuguese spelling changes a little.

With verbs ending in -r, -s, or -z:

• the final consonant drops
• the pronoun is attached with a hyphen

So:

• corrigir + lo → corrigi-lo

This happens with other verbs too:

• fazer → fazê-lo
• dizer → dizê-lo

So the r disappears before -lo.

The accent helps preserve the correct stress after the pronoun is attached.

Without getting too technical, when the final -r drops and -lo is added, Portuguese often adds an accent if needed to show where the stress should fall.

That is why you see forms like:

• fazê-lo
• dizê-lo

In corrigi-lo, the spelling reflects the standard attached-pronoun form after the infinitive.

It is fully grammatical and standard, but in everyday spoken Brazilian Portuguese, attached object pronouns like -lo are less common than in formal writing.

In natural conversation, many Brazilians would more likely say:

• vou corrigir o erro na mesma hora

That avoids the clitic pronoun altogether.

So:

• vou corrigi-lo = correct and standard, especially in writing or careful speech
• vou corrigir o erro = very natural in everyday Brazilian Portuguese

It means right away, immediately, or on the spot.

Literally, it looks like at the same hour, but in normal use it is an idiomatic expression meaning the speaker will do it without delay.

So the idea is:

• If I find an error in the report, I’ll correct it immediately.

Similar expressions:

• imediatamente
• na hora
• logo em seguida

Because the sentence begins with a dependent if-clause:

• Se eu encontrar um erro no relatório, ...

In Portuguese, when that kind of clause comes first, it is normally separated from the main clause with a comma.

So this is standard punctuation:

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

If you reverse the order, the comma is often omitted:

• Vou corrigi-lo na mesma hora se eu encontrar um erro no relatório.

Yes. Portuguese allows some flexibility here.

For example:

• Vou corrigi-lo na mesma hora se eu encontrar um erro no relatório.

This means basically the same thing.

You can also move na mesma hora for emphasis, though that sounds a little more marked:

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

The original sentence is a very natural, neutral way to say it.