Hi!
Not that the picture could be called clear and helpful for a diagnosis in any way but the milky white patch is a giveaway.
Welcome to 'boar glue', dried semen fluid that deserves it vernacular very descriptive name. It is a common problem with boars, especially teenage ones. while they can get boar glue anywhere, the nose is a very common place.
The patch will eventually fall off on its own or will come off when scratched. It may leave a little bald area if hairs stuck in the glue are ripped, but they will simply grow back.
More about boar glue and other boar problems in our Boar Care guide, which I would recommend you to have a look at:
Boar Care: Bits, Bums &