This is the factory reset procedure for firmware > 9.2.3. You can see your firmware version in the AirGradient dashboard under menu Hardware Administration.
Factory reset r firmware before 9.2.4
Please follow these steps to carry out a factory reset of the monitor:
Unplug the monitor from power
Put the monitor on a flat survace with the back facing upwards
Push the reset button with a small long device (e.g. a small screwdriver) and keep the button pressed
Power on the monitor (keep the reset button pressed)
Keep the reset button pressed until you see the yellow color. Then press the button three times.
If successful reset, LEDs will be green