If you have lost a working immobilizer key, you must purchase a new key blank and cut it to work with the ignition switch installed on the car.
Then follow the immobilizer learning procedure (see «Learning immobilizer keys»), by applying the existing training key and the new working key.
If the immobilizer learning key is lost, it is impossible to perform the key learning procedure. This means that you can continue to operate the car only with the existing working key. In case of loss and the remaining working key or if the immobilizer malfunctions, both the immobilizer and the controller will have to be replaced with new ones. After such a replacement, you can cut a new training key blank to work with the ignition switch installed on the car, and carry out the learning procedure (see «Learning immobilizer keys»).