If that mole is not growing in a week and not bothering your dog then there is nothing wrong with your dog. But if it is sore to touch and is surrounded with inflammation then you should be concerned and take it to vet. There is an infection of lips known as Lip Fold Pyoderma. It occurs in folds of the lip where upper canine teeth touch it. If it is the case then use Chlorhexidine Oral solution or use Hydrogen Peroxide two times a day to control the infection. If your dogs area does not heal within two or three days of this treatment then consult a vet.