"You need a makeover! you'll attend the dinner and pretend to be my fiancé okay?" Yoongi holds your hands as he drag you towards your room.

The dinner that he meant was the one he told you about his parents that's going to introduce him to his soon to be wife. it's am arrange marriage and he doesn't want it, so to stop it Yoongi is going to be needing your help.

So you pretending to be his as if a 'fiancé' could be a good idea.