This has most likely become our go-to dog focus game, and it essentially involves feeding your dog by dropping food from a height. For some reason, most dogs think food falling from the sky is the best thing ever!
Begin by placing your dog in a sit position, saying "Ready," and then dropping the treat or kibble a few feet above your dog; a good way to train is to feed him his entire dinner this way. By saying "Ready," you are priming the cue so that your dog knows something exciting is about to happen whenever you say it.
Be patient because it will take time for your dog to coordinate their mouth and position to catch the treat, and it's okay if they break the sit to get the treat; it should be a fun game. Just make sure they're sitting and looking up at you when you start dropping treats.
Try it both inside and outside the house to familiarise them with different environments. Once they appear to have mastered this from a sitting position; it may take days or weeks for them to learn the coordination, progress to dropping/throwing the treat while walking. This requires as much coordination from you as it does from them, and it will take some practise to get it right. Even if he misses it, hopefully he'll look for it on the ground and then look up at you for the next treat. A fun focus game to play anywhere.