he is missing his whole fin. The burn on his side has healed now but the fin is still a little stump.
That's tricky. Burned areas do not respond the same way as a nipped or torn area. Depending on how deep the burn, your finned friend maybe finless
Often fins grow back--i.e. if a fish is nipped badly, but only finage is damaged. However, if a fish is nipped to the skin (huge chunk of fin and scales missing), the wound heals, but the fin will not grow back (you often see that on larger cichlids who lived with nasty tank mates). Certainly clean water will help and adding Melafix (make sure it‚Äôs okay for Morays) to prevent bacterial growth on the wound.