Okay, after creating FrontWheel and BackWheel blueprints, I was able to get car moving. Have you reached that part of tutorial yet?
Additionally, your SkeletalMesh’s wheels are all aligned to wrong axis. You want to make sure your wheels are facing forward along X axis same as your car’s body. To see what I mean, open up your SkeletalMesh and open Skeleton tab. Under Skeleton Tree panel, click Body. You’ll see Red arrow pointing forward. Now click on one of wheels, and you’ll see arrow pointing to left. You want all to be pointing forward, same as Body.
Let me know if you get your car moving after setting up and assigning FrontWheel and BackWheel blueprints.