I'm not an expert on this, but since no one replied yet I will tell you some stuffs I know. I had bettas in the past that had ich. I used the ich cure bottles you find at any lfs or even walmart. For swim bladder, it only happened to one of my male betta. I fasted the betta for 2 days, and then fed him a small portion of a peeled defrosted pea. Fin rot can be also be treated with the medicine bottles. Overall, changing and maintaining good water quality does half of the job. I read about Dropsy, I don't know about the cure, since most fish usually die to dropsy. you can usually just search these up on google anyways. By all means, I'm not an expert. There's lots of experts out there on these diseases. I think there is more such as velvet and other stuffs.