Author: Jonathan Swain (aka "PurdueGuy")
7mm socket & ratchet
Installation is basically the reverse of removal, unless the backing plate comes loose. The backing plate is a thin metal plate between the headliner and the roof, which will normally stay in place if you don’t remove the headliner, but will likely fall off if you do remove the headliner. It has notches in it that line up with parts of the plastic end pieces, which you can see in this picture:
It can be a bit awkward, but once you line up the notches in the plate and get the screws started, everything will stay put.