How do I replace the flap for my Quick Fit door?

The Quick Fit Pet Doors have a flap that attaches to the frame using mounting screws and nuts that screw into a metal bar. The screws are removed and the new flap is screwed into the frame.

Door Size & SKU Replacement Flap Size & SKU
Small (P2-SW-11) Small Quick Fit Flap (RFA-104-11)
Medium (P2-MW-11) Medium Quick Fit Flap (RFA-103-11)
Large (P2-LW-11) Large Quick Fit Flap (RFA-102-11)