How to join:

If device in FN(factory new) state:

Press and hold button (1) for 2-3 seconds, until device start flashing led
Wait, in case of successfull join, device will flash led 5 times
If join failed, device will flash led 3 times

If device in a network:

Hold button (1) for 10 seconds, this will reset device to FN(factory new) status
Go to step 1 for FN device

How to add device into zigbe2mqtt

Use external converters feature

Converter file located here