This mini-app has been superseded by AC Rally Timing, in this app the reset key can be configured in app settings in Content Manager
Drag the file into Content Manager, confirm install, then go to settings -> Assetto Corsa -> Apps and activate the app.
R key will reset the car to the track (and invalidate laptime)
Prerequisites:
1. CSP must be enabled, with AI extension active
2. Works only in practice and hotlap - not in online sessions
3. track must have AI line
To change the key you have to edit the .py file.
To use a button on the wheel you probably have to use
ac.ext_isJoystickButtonPressed(controllerIndex, buttonIndex) instead of ac.ext_isButtonPressed
Controller index will probably be 0, 1 or 2; check button ID's in CM (screenshot in this post)
For instance: if ac.ext_isJoystickButtonPressed(0, 23):