Hi and welcome to the forum
Dropsy and bloat are the same thing. Basically the fish swells up and gets really fat over night or within a couple of days, the scales stick out from the body, the fish does a stringy white poop, stops eating and either sits on the bottom or by the surface or near a filter outlet breathing heavily.
The fish has an internal problem that is either a bacterial or protozoan infection or it has some sort of internal organ problem. Usually it is bacterial or protozoan.
If you can get some medicated fish food that might help. Metronidazole or another type of anti-biotic might help but work best if you can put it in food and get the fish to eat it. Bettas normally only live for a few years and the medication sometimes costs more than replacing the fish and some people would euthanize the fish, flush the tank out and start again.
If you want to use a medication like anti-biotics, you should treat the tank each day for a week (no more than 2 weeks) and clean the tank out each day (wipe the glass down, gravel clean and do a 100% water change) before retreating it. You should also do a good clean before you start any treatment to remove as much gunk as possible. The cleaner the environment the better the anti-biotics work.
Make sure any new water is free of chlorine/ chloramine before it is added to the tank.
Anti-biotics added to the water will wipe out filter bacteria so you need to monitor the ammonia & nitrite levels for a month after treatment. Medicated food is better in this respect because the food is laced with anti-biotics and the medication goes into the fish and not the water. If you feed with medicated food it is still a good idea to clean the tank each day for a couple of weeks.
If you can't get anti-biotics for a few days try cleaning the tank each day (wipe the glass down, 100% water change and gravel clean) and see if that helps. Sometimes it can.