This is a drill you can do at home, in the backyard, in your office — wherever you want — but it’s going to help you to shallow out your club. Standing about two feet away from the wall, pivot to the top of the backswing and get the club up against the wall.
You’re going to keep that clubhead against the wall for as long as possible, feeling your trail arm holding the club there as you start to rotate down and through. This will help you get the club behind you more in the transition to help shallow out your swing path.