Agree with previous recommendations to treat as wound in hospital tank until healed. If it does not improve (or actually worsen) in a weeks time; another possibility is that your frog has internal nematodes and one is living under the skin.

If that is the case; will need to take to veterinary for surgical removal and antibiotic. Read in your other thread you are/were also feeding it bull frogs. If those were wild caught; that is a possible parasite source and would also recommend a fecal test at vet. Good luck !