Graco Booster Seat Owner's Manual page 13

Step 8.
Attach elastic strap as shown 3 . If your elastic strap is
already attached you can skip to Step 9.
3
Step 9.
Flip seat over and insert the fabric from the head
support underneath the fabric on the lower back support
as shown 4
To make insertion of fabric easier, slide the upper and
lower back pieces apart by squeezing the red adjustment
button.
4
.
3
13