My angelfish got a big scar in his upper fin, how has done it?

get the betta OUT bettas and angels will fight angels fin nip and bettas if not trained to be less agressive first will attack the angel hence y ur angel is all messed up best bet remove the betta as he will kill ur angel even if the angel is way bigger the betta has the capability to kill it without even trying i'd take it out and rehome it if i were u