Pontiac 1998 Firebird Owner's Manual page 36

If the belt stops before it reaches the buckle, tilt the
latch plate and keep pulling until you can buckle
it.
Pull up on the latch plate to make sure it is secure.
If the belt is not long enough, see "Safety Belt
Extender" at the end of this section. 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.
3. To make the lap part tight, pull down on the buckle
end of the belt as you pull up on the shoulder part.
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