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I'm sorry to hear your dog has a cut on his nose. Make sure it isn't too deep or continuing to bleed, as stitches would then be required.
I would suggest getting some chlorhexiderm or betadine (iodine) from the pharmacy and making a 1 part solution to 10 parts warm water mix. Gently but thoroughly clean out this area very well, 2-3 times daily. Keep this area clean and open while healing up, and your dog will need to be kept indoors while healing to prevent further chances of bacteria build up in the cut. Pat dry after disinfecting and apply a thin strip of neosporin.
You'll likely need an oral antibiotic from your vet for best chance at healing if not starting to look better after a week or showing signs of other illness.
Best wishes, and let me know if I can help further.