Fortunately, his condition doesn't appear quite as bad as it sounded, especially if he's still eating. His swim bladder isn't making him swim abnormally at least, even if he's staying near the top.
This doesn't sound like a sickness, you saw what happened to him, he was beaten by by the zebra loach(es?) Those fish should never be kept together. Bettas are solitary fish and need their own territory, they don't belong in community tanks, especially with much larger and more aggressively territorial fish like botiid loaches! So he needs his own tank. A 5-10 gallon to himself would be much, much better than the community tank, or what he's in now. While he's in that container though, some things to help him recover...
How to help him heal:
Keep the water impeccably clean. Large water changes daily. Don't catch and move him to do water changes, just use a jug or cup to remove about 60-70% of the water, then refill the tank with clean fresh water after temperature matching it to the water in his tank, and using a water conditioner to declorinate.
Add a filter of some kind. A cheap internal filter or sponge filter will do, so long as it provides some water movement at the surface to allow gas exchange, and can begin cycling the tank/container. Remember that bettas are labyrinth breeders, so he will go to the surface a lot to breathe, and they build their bubble nests at the surface too. If you can provide some live plants and/or decor that allows him to rest on them while still being nearer to the surface, that is ideal for bettas, especially one recovering from having been knocked about by a loach. While labyrinth breathers can breath from the surface, they can still suffer from ammonia burns and nitrite poisoning, so changing the water daily - especially in an uncycled container with no filter or live plants - is essential!
Clean water with zero ammonia, zero nitrites, and low nitrates boosts a fishe's immune system, helping them to recover and to fight off any secondary infections.
Add more live plants (or fake as a second choice) both to process ammonia and improve water quality/give him things to rest on - but also to reduce his stress. Stress is the biggest killer of fish, and fish don't like to feel as if they're in the open and exposed to predators. They don't know that there are no predators! They feel safe with decor/plants and ideally floating plants overhead too, to hide among. I see some frogbit and red root floaters in the videos, from your other tanks? Add more to give him more overhead cover, and some more submerged plants if you can. Reducing his stress by making his environment calming will help.
To that end, also keep the lighting low, and add a background to the container he's in. Black paper or even a black plastic garbage bag taped over the back and one side will help him feel less exposed and safer, while you're still able to view and check on him. Feed him high quality food, and keep a close eye for secondary infections.