GMC 2010 Yukon XL Denali Owner's Manual page 76

There is one guide, if equipped, for each outside
passenger position in the second row seat and the
third row, if the vehicle has one. Here is how to install a
comfort guide to the safety belt:
Second Row
1. For the second row, remove the guide from its
storage clip on the interior body.
2-44
Third Row
If your vehicle has a third row, remove the guide
from its storage pocket on the side of the seat.