I've read early cases of mouth rot can be treated at home with a dilute iodine solution 1-2 times a day. You can dip a Q-tip in the solution and lightly wipe out the area of the cheesy, gunky stuff where the infection is. I'm not positive how long this treatment may last but I assume maybe a few weeks or until the infection seems to be completely cured (even if at that I would still apply the solution to the infected area for a few more days or so just to be sure it's completely gone).
With more extreme cases, a vet visit would need to be in order to also get oral or injection medication to fight off the infection.
I've had to do this treatment with a Blood python a while back for a couple weeks and it seemed to work nicely. I would keep the snake on newspaper, bump up the temps a few degrees, and make sure anything in the enclosure isn't too damp. Always offer fresh water as well. Keep us updated on how he progresses!