try putting the food down for ten minutes then take it away until the next feeding. To be honest dog's will eat when they're hungry, I've never known a dog to starve himself, intentionally, unless there was something medically wrong with it. He'll eat when he's hungry.
I had a dog that was picky, wouldn't eat regular meals, so if he didn't eat one day oh well, he ate the next day, some times he didn't eat for days or a week, but he always ate eventually. He had been like that since I have known him, I had tired everything, soaking it in water, chicken broth, mixing it with wet food, putting chicken or steak in it, green beans, even went so far as to getting different dog foods, you name I tried it, eventually I said enough he'll eat when he's hungry, and guess what? he did
If you don't want to do that for fear of "starving your dog", try soaking it in chicken broth, but he should eat when he's hungry. good luck