help with my injured angel

OK well i found a 5 gallon i had a cleard a spot for it luckily. i had a bag of gravel laying around so i put it in there. i put one gallon of the tank water in it and the rest is fresh. i took 3 fake plants from the big tank for the 5. it came with a lid and a biowheel filter thankfully. i took the smaller heater out of the big tank and put it in the smaller the angel is all transported. he looks a little happier. now the question is how do i heal him. do i put aquarium salt in it. do i do nothing. and he is just at the top swimming in circles. is he ok or is he a gonner

well he came from petco. he isnt really ill he just got bullied by a gourami and his dorsal fin and the fin in the back are all bit up. i just need to know how to fix it

well im really sad to say but i came home from dinner and ran right upstairs to check how the angels was doing and noticed he was upside down behind the heater and not moving at all :'(