Power off your Frigidaire microwave and unplug the unit.
Open the microwave door so you have full access to the hinges.
Pop the hinge covers (if there are any) off the door hinges where the door meets the microwave. Do this with the tip of a small flat-head screwdriver.
Tighten the exposed hinge screws with your screwdriver. If the hinges are damaged beyond repair, proceed to the next step.
Remove the screws on the damaged hinge and fit a new hinge in its place. Purchase a new hinge from Frigidaire or an appliance supply store.
Replace the hinge screws and hinge cover.