bblack07

Since I got a little confused with some of the descriptions in this thread I thought I'd add a little extra. I have a 2012 991.1 C2S, if it matters. I had 3 plugs per headlight in the frunk and the only one that was a horizontal oval that was a blue color on mine that clips in. I actually damaged a tab when I lightly pried it off but it's older so whatever. It turns out that one is lateral left and right adjustment. My vertical adjustment is actually the top black plug that easily opens and closes and is hinged. If you go to the bottom black plug that's to remove the headlight assembly entirely.

Anyways, I found this threat searching Google so the only point of my comment is to help clarify for others searching.
Top hole : Black plastic/rubber = Vertical headlight Adjustment with allen tool that was in my factory kit.
Middle Hole: Dark Blue plug = horizontal headlight aiming adjustment with the same allen tool
Bottom: Black Plastic/rubber hinge plug similar to the top one. This uses a different tool in the factory kit but with a quarter turn released the headlight assembly entirely.

Don't be a moron like me and crank on the middle blue one swearing that you are seeing minor vertical change then realize it's only moving left or right and not solving the issue haha.