Student or Learner
I would like you to imagine that there are two guys fighting and a third guy tries to calm them. Suddenly the police arrive and try to arrest the third guy as well then what would he say "I was trying to break their fight?"
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.
not a teacher
There are many possibilities, including:
I was trying to break up the fight.
They were fighting and I was just trying to break it up.
It wasn't my fight. I was trying to break it up.
I wasn't fighting. I was breaking it up.
I wasn't in the fight. I was trying to stop it.
PS: I crossed with emsr2d2