Buick 2007 LaCrosse Owner's Manual page 36

2. Slide the guide under and past the belt. The
elastic cord must be under the belt. Then, place
the guide over the belt and insert the two edges
of the belt into the slots of the guide.
36
3. Be sure that the belt is not twisted and it lies
flat. The elastic cord must be under the belt
and the guide on top.