I adopted someone elses sick betta,advice/experience or knowledge shared would be so greatly appreciated?

Bettas need at least 5 gallons ( about 19 liters). the heater is good and higher temps do isolate the bacteria. it kinda mimics having a fever. we dont really like it, but it helps fight the bacteria. to help with the stress of moving tanks, try to keep the room quiet and without a lot of activity. Having the lights of or slightly dimmed also helps with the stress. live plants are better, fabric is okay, and plastic is undesirable. especially in bettas. thinking more long term, live plants help with their health and they dont tear fins like plastic plants do. If your not already medicating him, i would start that, but do some research on the infections your fighting. i also dont know if medications work when used together so you might want to look that up too. Stress coat is also good for your fish and sometimes it de-chlorinates the water too. Hope your betta gets better!