Joystick Library Rotary Encoder Steering

Hi,
I'm building a steering wheel with the Arduino Leonardo and a rotary encoder using the joystick Library by MHeironimus.
I used the code I found here: https://www.hackster.io/immortalx/arduino-gaming-steering-wheel-f50d67
And if I testet it under "Arduino Leonardo properties" in Windows 10 it worked but it did not ingame (Farming Simulator 19). So I found in a youtube video (Windows 10- Steering Wheel, Logitech G29 Calibration & Centering Issue Fix - YouTube by 2:00 min) that it is a wheel axis.
So my question is what I need to write here

 Joystick.setXAxis(encoder);

that it will be the wheel axis (and hopefully work)?