To reset a Carrera 1/24 slot car is pretty easy to do. Put the car on the track and press the CODE button the number of times that matches the controller. So example if the controller you want to use is coded to two press the code button two times. In addition the cars front lights will start to blink letting you know the programming has started. Then you will need to press the front button on the controller. The car is now connected to the controller.
I spent two weeks trying to figure out how to change the code of one of my cars. The reset instructions aren’t that clear or easy to find.