Don't worry the first thing I would do is brush his teeth and make sure your dog always get checked up at a vet. And don't let him lick you no the face poop breaks your skin out . And most likely he will throw it up any ways.
Dogs often do this when food passes through their digestive tract too quickly to absorb all of the nutrients. They smell the poop, recognize the nutrient is still in it and eat it for a second go around so they'll absorb it. Always get your dogs their check ups because it could also indicate worms but it's probably not something you need to worry too much about. Just make sure to brush it's teeth often and I wouldn't let it kiss me on the face.