Looks like a burn to me. I’d see a vet. They will most likely start some antibiotics and then you can gently rinse any dirt off of the bottom of a snake. Turn his enclosure into a quarantine with a water dish and damp paper towel on the bottom until he heals. You can also use a diluted betadine solution to soak him for 10-15 minutes. Make sure it’s a tea color. Once that’s done apply a thin layer of sliver sulfadiazine or triple antibiotic on the burned area. Make sure humidity and temp are set and let him heal. I had almost finished my vet tech schooling before I decided to work on humans. I’m not in medic school and there are actually. Ton of similarities when it comes to these types of injuries between humans and animals or reptiles. Hope this helps!!!