Okay as far as I am remember I read it before

Jungkook was Jimin's best friend/good friend that likes him. But Jimin had a thing for bad boys which Jungkook is not himself.

So taehyung and the other members helps change Jungkook into a bad boy so Jimin can notice him. 

As far as I know it was a school au and it's either on asianfanfics or ao3