Do you have a close-up photo of the bump?

I agree, you best best is removal by a vet with a culture and pathology testing. If you have this done he will need a hospital tank for a few weeks to keep the incision clean while healing. Hospital tank can be just a 10 gallon tank with paper towels as flooring changed daily. Water bowl rinsed and water changed daily. It's likely they'll order an antibiotic ointment for the area after removed. We can guide you later as needed.

If the bump is an infection he will need systemic antibiotics by a vet and may also need topical treatment. If it's an infection it will need drained by a vet.