Power off your Frigidaire Electrolux microwave and open the door.
Insert the tip of your flathead screwdriver in the seam where the interior door lining meets the body of the door.
Work your way around the lining, prying it off as you go. Once removed, you will have access to the door sensor. It will be located next to the door latch and will be connected to wiring.
Check that the wiring is plugged into the sensor. If it isn't plugged in securely, unplug it and plug it back in.
Check the screws on the sensor and make sure they are tightly securing the door sensor. Tighten with a screwdriver if they are loose.
Replace the door lining when finished.