The fixed driver is now called the default driver and is set on the vehicle in Inventory, not on the license.
Change driver
You change the default driver on the vehicle's detail card in Inventory, on the User Access tab. See Change the default driver on a vehicle.
Change vehicle
If you have a new vehicle, or the GPS is to be moved to another vehicle, Autogear makes the change for you. That way, the vehicle and GPS are set up correctly for the vehicle model. See Add or change a vehicle.