I would bathe the affected tissues with hydrogen peroxide then freely rinse the area with betadine. Doing this every day for a few days should stop the spread of the infection and clear it up. If it doesn't you could try putting some neosporin on the tail for about ten days, but I think the betadine and hydrogen peroxide should work.
The snake will probaby heal and go through a couple of sheds. Since the tail is the affected area, you will probably have to be really careful about providing adequate humidity during the first few shed cycles to help it shed the skin from the tail tip.
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Chris Harrison
...he was beginning to realize he was the creature of a god that appreciated the discomfort of his worshippers - W. Somerset Maugham