suspected betta tb- what to do now

i work at a pet store and end of october i took home a betta that didnt look great and a 3 gallon tank. thats not the best setup but i figured he would pass there anyway and its what i could afford. i gave him a couple of plants as well.

i definitely have developed skin lesions from mycobacterium at work and i think i spread it to my fish because a few weeks into having him he grew tumors on his head. i didnt realize this diagnosis fully until now and i just assumed the lumps were cancer i couldnt do anything about. 2 months later he has been floating on his side or nestling himself in things like he has swim bladder but with the tumor things im thinking i probably spread tb to him ): it could be swim bladder too because i realized late in that the filter wasnt working well or i hadnt submerged it properly for a period of time so the water stats were bad (i know im bad for not checking sooner).

im sorry. i know its my fault but im wondering it i should euthanize and if so how, and if theres something nice i could do for him first.