Я исправил этот недочёт.

Исправил is the past tense form of the verb исправить, which means to correct, to fix, or to remedy.

In Russian past tense, a form like исправил literally means corrected/fixed. So:

• Я исправил = I corrected / I fixed

The ending -л is the normal marker of the Russian past tense.

In the past tense, Russian verbs agree with the gender and number of the subject.

• исправил = masculine singular
• исправила = feminine singular
• исправило = neuter singular
• исправили = plural

So Я исправил этот недочёт would normally be said by a male speaker.

A female speaker would say:

• Я исправила этот недочёт.

This is a very common Russian aspect question.

• исправил is perfective
• исправлял is imperfective

Here, исправил shows a completed result: the flaw/oversight has been corrected.

So:

• Я исправил этот недочёт. = I corrected/fixed this shortcoming.
  The action is completed.

By contrast:

• Я исправлял этот недочёт. = I was correcting this shortcoming / I used to correct this shortcoming / I worked on correcting it.

The imperfective version focuses more on the process, not the finished result.

Недочёт means something like:

• shortcoming
• defect
• flaw
• oversight
• deficiency

It often refers to something that is not quite right, incomplete, or done imperfectly, rather than a simple basic mistake.

Depending on context, it can sound a bit more formal or technical than ошибка.

A rough contrast:

• ошибка = mistake, error
• недочёт = shortcoming, flaw, thing that was not fully thought through or done properly

Because этот недочёт is in the accusative singular, and for masculine inanimate nouns, the accusative looks exactly like the nominative.

Here:

• недочёт is masculine
• it is inanimate
• it is the direct object of исправил

So the accusative is:

• этот недочёт

not

• этого недочёта

Compare:

• Я вижу этот стол. = masculine inanimate → accusative = nominative
• Я вижу этого студента. = masculine animate → accusative = genitive-like form

So этот недочёт is exactly what you should expect here.

Этот means this.

It has to agree with the noun in:

• gender
• number
• case

Since недочёт is:

• masculine
• singular
• accusative (same form here as nominative because it is inanimate)

the correct form is:

• этот

Other forms would be different with other nouns:

• эта ошибка = this mistake
• это письмо = this letter
• эти недочёты = these shortcomings

Yes. Very often Russian omits the subject pronoun when it is already clear from context.

So both are possible:

• Я исправил этот недочёт.
• Исправил этот недочёт.

The version with Я can sound more explicit or contrastive, for example:

• Я исправил этот недочёт, а он нет.
  I fixed this shortcoming, but he didn’t.

So Я is not always necessary, but it is perfectly natural.

Russian word order is fairly flexible. The basic meaning stays the same, but the emphasis can change.

All of these are possible:

• Я исправил этот недочёт.
• Этот недочёт я исправил.
• Я этот недочёт исправил.

Typical effects:

• Я исправил этот недочёт. = neutral
• Этот недочёт я исправил. = emphasis on this shortcoming
• Я этот недочёт исправил. = emphasis on I or on the fact that it got fixed

So the sentence is not locked into just one order.

Недочёт is pronounced with yo in the last stressed syllable:

• не-до-чёт

The letter ё is important because it tells you both the sound and the stress.

A useful rule:

• ё is always stressed

So in недочёт, the stress falls on the last syllable.

Also, in many Russian texts, ё is often written as е, so you may see:

• недочет

But it is still pronounced:

• недочёт

This is something learners need to watch out for.

Исправить is very natural with words like:

• ошибку = mistake
• недочёт = shortcoming/flaw
• опечатку = typo

It means to correct or to fix in the sense of improving something that is wrong.

Починить usually means to repair something physically or mechanically:

• починить телефон
• починить машину

So:

• исправить недочёт = natural
• починить недочёт = not natural

Another possible verb is устранить:

• устранить недочёт

That sounds more formal and means something like eliminate/remedy the shortcoming.

Yes, недочёт is countable. In this sentence it is singular because the speaker is talking about one specific shortcoming:

• этот недочёт = this shortcoming

If there were several, you would use the plural:

• Я исправил эти недочёты.
  I corrected these shortcomings.

So the singular here simply reflects the idea that one particular issue was fixed.