OMG I would be livid! Is the former owner at least going to pay the vet bill on the poor thing?
If you can't get a vet appointment immediately...
Baths in betadine tea (water + enough betadine to make it the color of weak tea) once a day will help ward off infection.
Neosporin/triple antibiotic ointment for a few days only since it's oil-based - eventually it will soften the scales and cause them to deteriorate and fall off. Use the kind without the topical painkiller.
Get your hands on some silver sulfadiazine cream. Normally it's prescription only from a vet or doctor, but I contacted
Mountainside Medical in NY a while back and they said they sell it without a prescription. Unlike neo/triple it uses a water-based cream so it won't hurt your snake's scales.
Paper towel as substrate, and keep the enclosure as clean as possible.