You don’t have to change anything on your system. You’ll have to understand, that the MQTT binding is a 1.x binding and as such needs configuration via config files rather than through Paper UI. Read more about it here:
Everything you need to know MQTT specific is described here: http://docs.openhab.org/addons/bindings/mqtt1/readme.html
An example about how this could look like with an example device:
- ITEAD Sonoff switches and sockets - cheap ESP8266 Wifi+MQTT hardware
- GitHub - arendst/Tasmota: Alternative firmware for ESP8266 and ESP32 based devices with easy configuration using webUI, OTA updates, automation using timers or rules, expandability and entirely local control over MQTT, HTTP, Serial or KNX. Full documentation at
Especially while following along the last link, you will realize that this is quite easy! Good luck!