Volvo FM Handbook page 197

186 Driving
3 Lower the truck to it's lowest level.
4 Press and hold in the lower part of the adjustment
button. Then press the memory button without
releasing the adjustment button. When the LED lights,
release the lower adjustment button first. Wait five
seconds and then release the memory button.
When the button is released the remaining air drains
out of the bellows.
5 When all the air is drained and there is no more
hissing, turn the starter key to the stop position.