To be sure that it's a wart you need to look at the color; it must be grey.
Ask your vet for better advices because some can go away just with time and some can be cancerous.
You need to be sure that it is not that bad and you can treat it by yourself but the vet is the best person to ask now.
What i can telle you is that is mostly comes from a lack of magnesium or stress so you can at least complement him with magnesium in his ration, it can't do bad.
I hope i could help you, good luck with it :)