How old is your dog?
What kind of dog is this?
Does the spot look like a wart with a rough surface or is more a smooth topped pimple type spot?
Is it up under the eye area or on the margin where nose meets muzzle?
With a sore in that spot in an middle aged dog I'd plan a vet visit for him as potentially it might be a tumor. It could also be a simple infection and you can try using some Neosporin or Triple Antibiotic ointment in case its from him poking his nose somewhere and ending up with a small infection from a puncture.
You mght also want to check here to see if it looks like a viral papilloma which can show up on the margin around the nose in addtion to along the lips and gums
You can also read here about more causes of lumps in dogs
Hope this helps you!