Hello! Installation is fairly simple but the OEM piece is hiding behind the driver's side rear wheel near the rear sway bar end link. The OEM headlight level link is highlighted in the photo below. The link is held in by two 10mm nuts.
Install the GWR headlight level adjuster but do not tighten the jam nuts. To properly adjust the head lights you'll need to lower the car back on the ground.
With the car on the ground you'll want to adjust the length until the arm is level with the pivot point. Once you've adjusted the link, tighten the jam nuts (indicated by the red arrows) and you are good to go. A couple notes on adjustment. If the arm is pointed UP you'll have your headlights aimed too low. If the arm is pointed DOWN, your headlights will be aimed too high and blind other drivers.