Hard to tell how deep it is & since it's been a while, a (herp) vet would be a good idea, IMO.
When a snake gets injured, they often shed more frequently as their body tries to heal...but ironically, the act of shedding can re-open the wound.
It's also hard to put a bandage on a snake, & when you apply a topical antiseptic, or also just the wound itself, can invite bits of substrate in the cage to stick to the
wound & cause trouble (promote infection etc). You should be keeping this snake on plain (preferably white) paper towels as substrate while he's healing & until the
vet clears him. Paper towels won't get stuck in the wound, but also any blood or oozing from the wound will show up on the towels...something you should monitor.
You need to keep him as clean as you can (change the paper towels when they get soiled).