The Reboot function is accessed from the > Options, > Advanced menu

Reboot is used during setup to make the vehicle scripts find and connect with each other, as well as tell the scripts to scan and update the linkset for keywords and apply settings for physics, lights, wheels, detect Passenger Prims and other systems.

After making changes to scripts or keywords during setup, you will need to reboot the vehicle.

Rebooting will not erase any controls adjustments made through the menu or directly in the Root Settings, it will simply reload your stored current values from the Root Settings, so there is no danger that rebooting the vehicle will lose your current values.