I've never done this adjustment so I'm going by the book here...
1. Loosen 2 carriage bolts “A” on each bracket located at the end of each guide tube.
2. Room is ready to be positioned horizontally by pushing on the outside, sidewall or by using a prying devise inserted into the opening between the room and coach.
Pages 9-11 of the manual
will explain more on how to conduct the horizontal adjustment.