Under the "Tick" tab in the left menu, you can terminate your agreement by click on"Remove vehicle." Select which piece / vehicle is applicable and check if you want to reuse the piece or not.

If you keep the chip, you can use it on a new car later, then remember to register a new car number when applicable. If you check that it will not be used again, you will get back the deposit for the tag and you can throw the piece as electrical waste.