Pretty easy actually. Don’t feed the dog in any kind of bowl. You have to feed by hand, one piece of kibble at a time. I’d one up it at the same time and train it while you do this. Sit, lay down, stay, go the cage, etc. Whatever commands you want trained. Measure out 1.5 cups of kibble and do that twice a day. You can throw down a few pieces at once but you get the idea. I’ve had to retrain a bunch of rescues this way and it works every time. Some of them just refuse to train and will sacrifice the food but in the end they always lose and finally give in.

You can also buy a Kong and stuff kibble in it to make the k9 work for its meal.
https://www.amazon.com/KONG-Cl...la-353353134139&th=1

Our Golden Retriever has been like that since he was a pup and is now almost 7. He gets fed twice a day and if there is food left in the bowl after 60 seconds it's shocking and at this point concerning. I've never had a dog get as excited about food as he has. The only time he won't eat is when he's traveling with us, however once we get to our destination he's good to go again and we just ease him back into the food by giving smaller amounts for the first meal.