There were several tutorials when I did it, not sure which one exactly I have followed.
Basically you need:
A MQTT server (can be installed via openhabian-config), the MQTT binding and Zigbee2MQTT installed on the device where your zigbee stick is attached and new OH things based on the mqtt binding and no longer using deconz binding.
As far as I understand you cannot use deconz software and zigbee2mqtt in parallel and would need to repair your devices, therefore not sure if you want to go this way.