When a dog has not teeth then they won't be able to eat any hard dry dog food and you'll have to feed the dog some canned dog food instead since it's soft and easy for them to eat when they have no teeth.
You may also be able to add some water to some small dry dog food which will soften it up better and make it easier for the dog to eat without teeth.
Or take some chicken or other meat and blend it up to make some soft food for the dog to chew with no teeth but just make sure it's blended up easy enough for them to swallow.
Some raw hamburger meat can also be easy to chew for a dog who has no teeth but only feed the dog the raw hamburger meat in moderation and not as an all the time food.