betta fish bloating

Hello. One of my two betta fish has a swollen side and is not moving much. She also has not tried to eat any food I put in her hospital tank. She has trouble swimming such as she can not turn correctly or move properly because her left side is swollen. I first I thought it was constipation...

I have two betta fish, and they both bloat easily. I can feed them three pellets and all of a sudden their bellies are swollen. Does anyone know how I can help them ease their bloating?