Try adding a little water to his kibble and warming it in the microwave for 10- 15 seconds. That usually works. If that doesn't work then then add a small amount of garlic powder and some water to his kibble and microwave.
*Do not use fresh garlic or garlic salt. Garlic isn't really good for dogs, (altho you do find it in some dog treats) but a little garlic powder is fine. I guarantee it will work.