You can map the buzzers to any input device such as a controller or real buzzers, the controllers needs to be connected.
- Open `RetroDECK Configurator`
- Open `PCSX2`
- Go to `Settings` -> `Controllers` -> Select `USB Port` -> Select `Buzz Controller` from the Dropdown list
- Map each players `Red`, `Blue`, `Orange` and `Green` buttons to the controller or input device they are using by clicking on each value and pressing the button you want to map.