That looks like either an injury from being left alone with prey or a burn from getting too close to an unregulated heat lamp... Maybe even getting caught on a piece of dangerous decor or something. UTH burns and scale rot are almost always on the belly.

Until he gets to the vet, replace the bedding like was suggested. I'd recommend paper towels; it's easier to keep track of bleeding/fluid/discharge on those than it is on newspaper.

As for the actual wounds, betadine is good, and chlorhexidine works as well (it's a bit milder when you're going to be using it long term IMO). First thing is making sure the wounds are cleaned out. You don't want bits of bedding caught in there complicating the healing process. You can make a solution of either betadine/chlorhexidine and water and use that to kind of wash off any debris in the wounds. Then, if it was me, I'd probably quickly swab the wounds with that solution at least once a day until he gets to the vet to try and minimize the risk of infection.