Silvadene creme seems to work best on burns like this, but you will have to get it from the Vet ! Please ask the vet about that.
Until then, keep the snake very clean. Either un-printed news paper or white paper towels. Keep the stress low.

Absolutely control the UTH now. There is no waiting on that. There are thermostats for $20 on Amazon, Jumpstart is a brand that can be used until there are funds for something better.

Provide a lot of privacy for the snake to keep stress down, black out the sides, back and top of the tank, creating a "cave" of sorts. You can tape dark paper on the outside of the tank.
See if the vet will let you buy some Silvadene ahead of the appointment if you share pictures and talk to them. The sooner you get some proper treatment on that, the better ..