While not sure about this specific issue, it does look painful.
Make sure the water quality is ideal for them. Number one concern. Maybe a way to get this guy separated from the other two and hope for some healing?
I always use Epsom Salts (ES) - magnesium sulfate. Plain with no additives like oils scents, etc. Available at the Grocery or pharmacy.
Here is some info about how it treats wounds (albeit a differing method and subject) Mainly information is on the top second column. Basically just says it aids healing and recovery of septic wounds. (lol, but it is scientific fact not just anecdotal evidence)
https://www.ncbi.nlm.nih.gov/pmc/art...168986/?page=2
You can use up to a tablespoon per gallon which I have used in tropical fish. Cichlids are used to more "salts" / minerals. Not sure if anyone else has used a greater dosage.
You should add the concentration to cleaned excellent tank water, gradually over a day or 2 and then you can make a concentrate to use while doing
pwc's. Generally I would divide the initial doses into 4-6 portions adding in every 8 hours.
I would keep the concentration for a treatment period of about 2 weeks. Then as future
pwc happen, just omit the ES and return to your normal water.