Picky dog

Does anyone have tips on how to get a stubborn dog to eat?

My 5 year old French bulldog just recently stopped eating his food, he’s been on this food for years due to his allergies. We have gotten him to eat by putting a little topper on the food but we are going out of town and have 6 pets.

I don’t want to overwhelm the dog sitter because she’ll be bringing her three young kids with her too so I’m trying to make the instructions simple, especially since he’s food aggressive towards our other dogs (work in progress).

I don’t want to switch foods because it’s difficult to find grain and chicken free pet food.

Btw: we tried crating him while eating, he refused to eat. We tried picking the food up after 15 mins, he doesn’t care. We tried less topper, more food, he just ate the food that had topper (literally spent 30 minutes picking each piece and leaving the plain food). I even tried fasting him for a day incase it was a stomach ache causing this pickiness, the next morning he still refused to eat until there was topper.