Can anyone help me (tell me how to) properly align my headlamp assembly?

I took mine to a bodyshop and they did it in about 10 minutes.

Start out with a flat surface, and preferably a white wall. Pull your vehicle up to the wall, and mark where the geometric center of your low beam headlight for both headlights is on the wall, and then put a large piece of horizontal tape there. Back your car up 25 feet, and notice where the beam is hitting the wall. The beam pattern of a 1998 Blazer looks something like this ___|---|___ where there is a large rectangle of light, and then a somewhat even distribution of light off to both sides. The center of that rectangle should be right in the middle of your marking.

1998s don't require aligning. They should be install and screw in.

No, every headlight needs aligning. I've seen 98+'s driving around with one headlight pointed to the sky. Things as simple as changing the bulbs in these could require realigning

they need aligning, there are two alignment screws in them, one horizontal, one vertical, scomp gave good directions on how to' not sure of the size, but its a small socket that you need, youll see the cutouts, just pop the hood and they are ubove the lights