Below is the spacer that keeps the hitch from wandering back and forth in the track.
Rotate the hitch until the guide pin is out of the center track. Tighten the nut pictured below until the hitch can no longer move into the straight position. Start backing off that nut until the stopper backs off just enough for the hitch guide pin to easily rotate through the track.
The guide pin which is directly below the nut pictured below
should look like it is rolling on the rear of the track through the center of the hitch rotation. Hopefully this should work for you.
BTW, the hitch comes from the factory with the stopper all the way in so the hitch cannot rotate during shipping. I hope the installer didn't think that it was a packaging piece and completely removed it.