MY BETTA FISH IS SEVERLY WOUNDED AND NOT EATING, WHAT SHOULD I DO?

my betta fish got attacked by my cat yesterday and i found him on the floor, i put him back in his bowel and put a tiny drop of melafix in, now i know that melafix is bad for them and i plan on switching to beta fix tomorrow. he has a large gash on his head where pink flesh is exposed and some rips in his fins. he is just kind-of staying at the bottom of the bowel and only coming up for air. he seems to be only swimming around the side on the bowel against the gl i think his eyesight might be damaged or something because he is not getting the food have i put in? could he have brain damage or something? or is he just scared? i don't know what to do. i was going to change half of his water. how can i get him to start eating? are there any other suggestions you have about his eating or wounds! your help is greatly appreciated!