For one thing, I would not swing out of my shoelaces as much as Chavis does. That is not helping him as it only makes the holes in his swing that much larger. Then I would work on why he simply is hopeless on FB's from the waist to the top of the strike zone. That is a massive hole in his swing and virtually any ML pitcher can throw a FB between the belt and the top of the strike zone. If you can't hit a FB, you don't belong up here.
Once he closes off that hole in his swing, however long it takes, then he can start working on the low and away which also eats him alive. If he tries to work on both at once, he will fail. If he tries to work on the low and away before solving the FB from the belt to the top of the zone, he will fail. Gotta' figure out how to hit a FB first. Might be too anxious. Might be too concerned with hitting every ball a mile. I don't even think he is seeing the ball because he is missing it by a mile, usually swinging when the ball is past his bat and virtually in the catchers mitt. He almost looks like he is looking to see where he hit it before he hits it.