This tells us that the dog is using food to get its own way. Always feed your dog after you and your family have eaten, so that he knows there is no other more exciting food coming later. Put a small portion of the food you wish to feed in his dish and put it down in a quiet area. If he eats it, then praise him and pick up the dish - do not offer any more food until the next feed time. It is best to feed twice a day.
Next mealtime do exactly the same.
If he eats it all, then gradually increase the amount fed until he is eating the required amount. Never leave the food down for him to pick at - this is often the cause of a fussy feeder. If it is not eaten, do not comment on it but simply pick it up. The next mealtime put a small amount of food down again for five minutes, and pick it up. Your dog may hold out for a couple of days, but he is not stupid and will realise that as nothing else is on offer he had better eat the food while it is available.