Sis's dog never had much of an appetite at the best of times and he was very reluctant to eat also.
Some tricks I've tried to get them to eat:
Try offering only very small amounts of food, far less than they should eat. A lot of food on a plate or bowl can be overwhelming.
Try putting it on one of your own dinner plates.
Try offering food in a place you don't usually feed.
Try dropping food on the floor as if by mistake.