I should add you need to install Mqtt broker from the addin store as well.
Once you get this installed under integrations you should see Mqtt and this is where your new ZigBee devices will be listed. (As opposed to the ZigBee integration)
No need to hard reset the thermostat as once you add it through zigbee2mqtt and get mqtt integration added the device will be new to your HA installation.
sabreW4K3