Adopted a fish tank, molly has a white spot.?

not to sound horrible or really straight forward but my fish had white spots then turned white which could be a disease that i think is called cotton diseas or something like that it can be very harmful, both of my fish got it and sadly ped away but i think you can get something to sprinkle in the water to get rid of the disease from a locqal pet shop or the vets, i hope this helped.