Please note: Information in this post is not meant as a substitute for veterinary care. Always consult your veterinarian in an emergency.
Remove any dirt or debris from the wound. Wash the wound with clean water or saline solutions. DO NOT introduce anything harmful into the wound like soap or hydrogen peroxide. Use firm pressure if needed to stop the bleeding. DO NOT use a tourniquet.
Monitor the wound for any infections. I recommend you call your vet and take your dog in to make sure the wound does not get worse.