Buick 2008 Allure Owner's Manual page 316

Locate the vertical headlamp aiming screws under the
hood near the headlamps.
The adjustment screw can be turned with a
6 mm male hex.
5-56
To adjust the vertical aim on the headlamps:
1. Open the hood. See Hood Release on page 5-11
for more information.
2. Locate the aim dot on the lens of the low-beam
headlamp.
3. Measure the distance from the ground to the
aim dot on the low-beam headlamp. Record the
distance.