Hi!
It is impossible to tell from your picture but it may be that your boy has simply stuck his nose where he shouldn't have, potentially some boar glue (semen fluid). In this case, you will have to wait until the hair/scab is coming off on its own as the common name for dried semen fluid is VERY descriptive.
Please see a vet if the area gets worse or there is a growing balding area with crusts on it (potential fungal).