Do-It-Yourself Story

First, I removed the flap spring attached to the bottom hinge. Then I had to pop off the lower hinge cover so the old hinge could be removed. It doesn't seem designed to pop off so I had to wiggle and screwdriver blade under it to get if off. Fortunately, I didn't break off any of the plastic nibs that hold the cover to the flap! Then I realized that the hinge actually slides onto a support on the frame of the door and the only way to get it on and install it into the flap was to take the whole flap off the door. I was initially stymied because the screws that were easily visible in the YouTube video I found we covered by screwcaps on my unit. Turns out they were easy to pop off with no damage. Once I unscrewed the flap from the door I could slide the hinge onto the support, place it in its proper place in the flap, re-attach the flap and screwcaps, and then re-attach the hinge spring. Voila! I did not replace the upper hinge. I was unable to remove the hinge cover, but I also realized the door functioned just fine without the upper hinge (there's no spring up there).