Unplug the microwave or remove the power supply at the circuit breaker.
Remove the screw on the left side of the plastic light cover and set it to one side. The plastic cover hangs open, revealing the light bulb.
Unscrew the burned-out bulb carefully; the glass may still be hot if the bulb was recently working.
Screw in a suitable 30-watt incandescent replacement bulb, lift the cover and replace the screw.
Reconnect the power to the microwave. The light is now ready for use.