How do I know if I should put my betta fish, with swim bladder disease, down?

I just got my betta fish a little over a month ago. When I first brought him home he was floating on his side at the top of his cup. At the time I didn’t realize that was a symptom of swim bladder disease. I got my 5 gallon tank set up, conditioned, cycled, and tested the water.

I realized that he never swam down and always just floated at the top so I researched it and found out he has swim bladder disease. So I cleaned his tank again, didn’t feed him for 3 days, and tried to give him peas which he wouldn’t eat (I had to use a toothpick because they would sink and he can’t swim down). After 3 days of trying to feed him peas I cleaned his tank again and added some aquarium salt. I’m not sure what else to do and there has been zero change in his behavior.

He also is quite small and I don’t think he is full grown, so I’m not sure if his swim bladder is fully developed or what. I hate to see him just floating on his side and I don’t want him to develop sores from the air. I’m not sure if euthanizing him is the next step or if there is something else in his best interest instead.