Hi Welcome to Fish Lore

Poor little guy. I'm sure you're worried about him.
First, I'd suggest you read this:
Betta Care Guide - Please Read First!!!
and this:
Nitrogen Cycle
It would really be a good idea to get your
betta into a nice heated cycled tank. I prefer a minimum of 5gallons but some members have them in 2.5.
If you can get Fish Protector, Vita-chem garlic guard and keeping his water very clean, this combination should help him heal if he's not injured internally.
We've had other bettas on the forum jump and this worked wonders.
Good luck, I hope he feels better soon