Hi there. I'm so sorry your fish got dropsy.
First, Dropsy is incredibly difficult to treat, and most opt for euthanization at the sight of it. I've only successfully treated Dropsy once, and that was when the pinceconing was only behind the gills, but the fish was so swollen she had a lower grade pop-eye on one side. By the end of treatment, only 3/4 of the scales had pinceconed. They will continue to pinecone for the first few days of treatment, and since it moves so fast, most don't make it. I'm very sorry about your fish.
If you want to try to treat it, the best way to treat it is to get Kanaplex and some unscented epsom salts.
The epsom salts buy time, the kanaplex will take care of any bacterial problems in the kidney, as Dropsy is kidney failure.
Epsom salt draws out fluid buildup, and can help slow or even reduce the swelling. In my experience, it just slowed down the swelling and gave the kanaplex time to work. Kanaplex is a 6 day treatment, dosing every other day, so three dosing days, and my fish didn't show improvement until 3 days after the treatement ended. Also, I recommend doing different than the package dose. Day 1, do a full dose. Day 2, do a 50% water change and do a 1/2 dose. Day 3, full dose. Day 4, 50% water change and 1/2 dose. Day 5, full dose. Day six, 50% water change and 1/2 dose. Day seven, leave it be.
So, you'll want to add 1tbsp per 5 gallons of epsom salt to the main tank. Dissolve the salt before adding it, and add it slowly. It does not increase salinity, but will increase TDS and gH rather quickly, which can shock some fish. Yours should be fine though. You will want to do 2-3 (3 is better) epsom salt baths each day.
For the baths, dissolve 1tbsp of epsom salt in one gallon of water. Move your fish in for 10-15 minutes. If your fish shows signs of severe discomfort (rolling on side and unable to right itself, sitting on the bottom and unable to get up, or defecating) remove your fish immediately.
Kanaplex is the key here. There are a couple of different types of Dropsy; bacterial, fungal, parasitic, and organ failure. Bacterial is most common, and that is what kanaplex will treat. Fungal and parasitic are difficult to treat and diagnose, and I'm not sure how to treat them. If it's organ failure, the only reported treatment has been epsom salt, as it reduces fluids and therefore pressure on the kidneys, giving them a chance to heal.
Best of luck.