Diagnosis
F1 and F2 are fault codes for the oven temperature sensor circuit. F1 usually means the sensor is open (broken wire or bad sensor), F2 means it's shorted. This sensor monitors internal temperature for safety.
How to Fix It
Unplug the microwave. The sensor is a small, white ceramic-looking component with two wires, attached to the side or top of the interior cavity. Carefully check the wires for any obvious breaks or burns. If the wires look good, the sensor itself is likely bad. You'll need to desolder the old one and solder in a new, exact replacement sensor. It's a delicate job.
If That Didn't Work
If the sensor and wiring test fine with a multimeter (it should show a specific resistance, often around 10k ohms at room temp), then the main control board is faulty and not reading the signal correctly. Board replacement is the next step.
Heads Up
Don't ignore these codes. The microwave has locked itself out because it can't guarantee safe operation. A reset by unplugging might clear the code temporarily, but it will come back until the underlying sensor or board issue is fixed.