This forum is for saltwater, so you may get better answers on a freshwater forum, however this looks to me like a secondary fungal infection. Melafix is just tea tree oil, it can help avoid and treat minor infections however Id strongly recommend Methylene blue for this level of infection.
Wiping it off won’t do much except stress the fish out and possibly add more foreign bacteria to the wound.
If you can get Methylene blue I would dose 2 drops per gallon, dosing every other 50% water change. Methylene blue does not biodegrade in the tank so no need to dose it daily.
I would also highly suggest water changes every 2-3 days, a 50% and make sure that the temperature of the new water is the exact same or within 2-3 degrees of the tank water.
What size is the tank, and does it have a filter?
Do you know your parameters? (Ammonia, nitrite, nitrate, temperature etc)