Depends on the severity. If it's just brown tinges on the scale tips, the soaking the snake in chlorhexidine gluc. or betadine(chlorhex doesn't need rinsed off), and then lubing the snake with polysporin or sulfadene will work fine.

If it's to where the scales are flaking/falling off/have an odor, then the snake will need some injectable meds along with the above treatment.

I've had one snake come in(none in my collection in these 4, almost 5 years of keeping them) that was burned severely on the back 3rd of her belly. The scales were edematous(collecting fluid). So I poked open every scale with a sterile needle, scrubbed her belly gently but firmly with chlorhexidine, then lubed her up with polysporin. She got put on newspaper and had a very small water bowl(3" ceramic souffle dish) for a few weeks. I washed her in soap and water every few days just to keep her clean and to reapply the polysporin. She healed up wonderfully and went to a good owner here on the forum(prototypePythons).

I've never had a case of belly rot here, even if the snake has tipped its water bowl and peed in the water and sat in it for a day and a half. Get 'em wiped off and popped in a clean tub and they are fine. Takes a long time in an extremely dirty enclosure for belly rot to form, unless the snake has a lowered immune system and is just prone to infection.