Here's how I'd do it.
1 - Visit your hearth shop & buy a tube of gasket cement & the correct sized gasket for the door. in their manuals, Harman does not list this item by length and diameter, but you should need 7 feet of 3/8" diameter fiberglass rope. You may find the correct size cheaper online.
2 - Remove the door & lay it on a flat surface strong enough to support it & protect the door by placing it on cardboard or a towel (or the like).
3 - Remove the gasket from the door channel. It should just pull out.
4 - Using a rounded scraping tool, remove all the gasket cement from the channel. I have a bunch of old flat head screw drivers (in different sizes) that I rounded off for this purpose using my bench grinder. For stubborn areas, don't be afraid to chip the cement out by hitting the handle of the screwdriver with a hammer.
5 - Once the channel is clean, wipe any excess dust out with a wet rag. Dust will compromise the adhesion of the new casket cement.
6 - Lay a small bead of cement in the bottom of the channel & using your pinky or a small piece of gasket, smear it to cover the entire channel groove
(sides & bottom).
7 - Lay another small bead of cement in the channel.
8 - Using a sharp pair of scissors, carefully cut one end of the gasket material square.
9 - Starting in a lower corner of the door, lay the gasket along the channel & press it into the cement bead. **DO NOT STRETCH THE GASKET.**
Work your way around the door channel until you get to the origin. Carefully trim the end to length so that it butts TIGHTLY up against the origin when the end is pressed into the cement bead.
10 - Work your way back around the gasket & make sure it's pressed nicely into the channel.
11 - Use a wet towel to remove any cement that has gotten squeezed out of the channel before it sets up.
12 - Carefully replace the door onto the stove, close it & latch it. Leave it for a day if you can, so that the cement dries.
Others may do it differently, but this method has worked well for me.