If it contains scenery data (airports or regions), move the folder to: X-Plane 11/Custom Scenery/ .
Since .rar is a compressed format, you must extract its contents before X-Plane can use them. X-Plane-11-TRNT.rar
The installation path depends on what is inside the .rar file: If it contains scenery data (airports or regions),
Plug your joystick directly into your PC (avoid hubs) and calibrate it in the Settings > Joystick menu before your first flight. X-Plane-11-TRNT.rar