In the event of loss, theft or suspicion of misuse, for security reasons you should immediately block your activated device for use of the Access app. Contact E-Banking Support at 0848 848 064.
If your smartphone reappears, Support can easily lift the block. You will not need to register again.
If the device is actually lost you can easily deactivate the Access app in E-Banking under "Settings > Security" or "Offerings > Means of access".