Aston Martin DB11 Owner's Handbook Manual page 61

Pull upwards on the diagonal belt to make sure that the latching
is secure and to remove all slack from the belt.
Check that the lap belt is installed snugly, low down across the
hips, and that there are no twists.
If it is necessary for a passenger to adjust their seat or seating
position during a journey, the belt tension might be disturbed.
The passenger should therefore (as soon as it is safe to do so)
gently pull down the shoulder run of the seat belt to create some
slack and then immediately release it to re-tension the belt for the
new seating position.
Seat Belt Unfastening
Push the button on the buckle. While holding the seat belt
buckle, allow the belt to slowly retract to its stored position.
Warning: Do not allow the belt to twist, or be looped,
frayed or obstructed in any way when the seat belt is
retracted back into its stowage position.
3.15
Before Driving