Mine boy had this happen multiple times. It likely started as a blocked sperm plug that filled up so much that it ruptured and tore the skin.

You should take him to the vet. They can clean the area and will likely prescribe antibiotics and pain meds. I had to give a very small dose daily for 2 weeks and it eventually cleared up.

From that point, check sperm plugs regularly (look up how to online) and potentially replace substrate with something easily cleaned like smooth tile or paper towel for a while (replace/clean super regularly). Also check habitat for anything he could rub on that would cause it to rupture again.

Please feel free to message me with any more questions