Chevrolet 2004 Astro Owner's Manual page 34

When you sit in a center seating position, you have a
lap safety belt, which has no retractor. To make the belt
longer, tilt the latch plate and pull it along the belt.
1-28
To make the belt shorter, pull its free end as shown
until the belt is snug. Buckle, position and release it the
same way as the lap part of a lap-shoulder belt. If
the belt isn't long enough, see Safety Belt Extender on
page 1-34 .
Make sure the release button on the buckle is positioned
so you would be able to unbuckle the safety belt
quickly if you ever had to.