Typically the Vanquish LED headlight conversion won't require any adjustment if the globes have been installed correctly, as the beam pattern is maintained when changing from halogen to LED.
If a headlight alignment is required after installation the easiest way to achieve accuracy is as follows: Park your vehicle on level ground approx. 5 metres away from a flat vertical surface - your garage door may work.
Turn on low beam and mark the height of the beam on both left & right side with some tape. Remove one of the LED globes and refit an original globe. Covering the new LED globe with a towel, see if the height of the original globe differs from the height you marked on the wall.
If adjustment is required, open the bonnet and you should find two adjustment screws at the back or top of the headlight housing (refer owners manual). Adjust the height until the height of the beam lines up with the tape you placed on the wall. Reinstall the second LED globe and repeat.