You're going to want to do probably 75% daily water changes, 100% if you can and your tank isn't cycled. Clean, warm water is a big key in treating fin rot.
I like to try a mild treatment before I attack it with potentially unnecessary medications, so I would do an aquarium salt treatment. 1 tsp per gallon, predissolved in some tank water. Basically what you want to do is get a glass of water from the tank and measure out however much salt you need into the water (if your tank is 5 gallons, then 5 tsp of AQ salt). Stir it until it's all dissolved. Then add the glass of salt water back to the tank slowly over the course of about an hour - so like 1/4 of the glass every 15 minutes or so.
If you have access to some stress coat, that's helpful too - use the double dose as recommended on the bottle :) I hope that helps!