Scooter harnesses are for working, not playing. When you snap the tugline to the harness, the dog should work in front of you with no sniffing, peeing or socializing. If you want your dog to relax and be offduty or to walk politely beside you, snap the leash to the collar.
Attach a light “drag” such as a bicycle tire to the harness with a line long enough for the drag to be comfortably behind the dog. With leash to collar and drag to harness, go for a walk. Drag on various surfaces.
The dog learns to pull, learns to be comfortable with something dragging behind him.Gradually drop back until you walk behind the drag instead of next to the dog. Practice the scooter commands. Teach “line out”