DIAGNOSIS The bulb is likely failed. This model uses a standard 25-watt T7 halogen appliance bulb, not an LED.
FIX Unplug the microwave. Remove the two screws from the bulb cover inside the cavity. Gently pull the cover down. Unscrew the old bulb counter-clockwise. Replace with a new 25-watt T7 halogen bulb (120V). Reinstall the cover and screws. Plug in.
IF THAT DIDN'T WORK Verify the bulb is seated correctly. If a new bulb also fails, the issue is the socket or door switch activating the light circuit. This requires professional service.
HEADS UP Do not use a bulb with a higher wattage. It can damage the wiring or lens cover. Ensure the unit is completely unplugged before attempting replacement.