I recommend doing a 75% water change, clean the gravel very thoroughly, and wipe down the glass with a clean fish sponge. Add carbon to the filter to deactivate the meds. I recommend doing a water change every day for a week, but that might be overkill. Also, were there any other fish in the tank with the infected fish?
If there were others in the tank with the one infected, they are at high risk of being infected too. Do a 75% water change and a gravel clean every day for a week. Wipe down the sides of the tank with a clean fish sponge. If the filter hasn't been cleaned in the last 2 weeks, do so now. It might sound like a lot but this is the only way to make sure your other fish will be safe from the infection. Best of luck!
Pictures of the remaining fishes so we can check them for diseases?
Have you tested the tank water for ammonia, nitrite, nitrate and pH?
If yes, what were the results in numbers?
What symptoms did the fish have before treatment and when it died?
Wipe the inside of the glass down with a clean fish sponge.
If you are certain that no other fish are sick, do a 75% water change and gravel clean the substrate every day for a week. This will dilute any medication and disease organisms that are in the water.
Make sure any new water is free of chlorine/ chloramine before it's added to the tank.
Clean the filter if it hasn't been done in the last 2 weeks. However, if the filter is less than 6 weeks old, do not clean it. Wash the filter materials/ media in a bucket of tank water and re-use them. Tip the bucket of dirty water on the garden/ lawn. Cleaning the filter means less gunk and cleaner water with fewer pathogens.
Monitor the remaining fish for the next couple of weeks and if there are no more problems, get another fish if you want. But wait at least 2 (preferably 4) weeks before adding any new fish, after a fish has died.