Tiradentes var en vigtig del af ent oprør Ii Minas Gerais.

Differencing between "en" and "et" is probably one of the most difficult things to do.. Since their are no destinct rule to help before you know a lot of words and how to bend them or if you have dictionary with you...
This is the rule:
*If the word coming after ends with -et when bend then use et
If the word ends with -en then use en. Sound easy, but then you need to know how the word is bend.. For that there are no rule. You just have to know.
Eks:
Hus -> huset -> et hus
Mus -> musen -> en mus

In this case:
Oprør -> oprøret -> et oprør

Før Brasiliens uafhaænginghed var der nogent oprør Ii landet.

Differentiating nogen/noget..
Nogen: someone
Noget: something
Here it references to oprør
Oprør is "something that you do"

Regeringens soldater fik fat afi Tiradentes.

After "fat" you will normally only see "i" or "."

Han blev dræbt Ii 1792.

In Danish we don't use capital letter I like in English. It looks like a stroke in the air seperating the words.

Engang var han regeringens fjende, men Ii dag er han viset som en helt.

I'm guessing that you mean he is 'seen' as a hero.. Unless it's a rare case where he is directly 'shown' as a hero.. I wouldn't know😌