Get the double sided tape and apply it to the shorter end of the garage door seal. Leave the cover on the tape on the side that's not stuck to the seal on for now.
Thoroughly clean the bottom of your front bumper so that it's spotless. Any dirt or grease will hinder the adhesion of the tape.
Pull the some of the cover off of your homemade lip bit by bit as you apply it to the bottom of the front bumper. Make sure you line up the edge of the lip with the edge of the bumper.
Once attached cut the excess of your lip kit kit off with a box cutter and a straight edge such as a ruler or anything else that has a straight edge.