Per the Manual
9. Install the rear bow in the side rails, and hook the two rear bow retainers to the bow and the roof rear rail.
10. Install the other roof bows from the rear toward the front of the car.
Step 7 has you removing the bows from the front and when you get to the rear. It says, At the rear bow release the two rear bow retainers from the roof rear rail.
unfortunatly the picture doesn't show what these retainers look like