Log in to CalNet with your usual credentials. When the 2-step verification is prompted, click other options. At the bottom of the list of your existing devices, click manage devices. Complete the verification with an already registered device or saved passcode. Once you verify your identity, you will be able to manage your devices. Please refer to this link to register your new device.
After these steps, you should have successfully added a new device. If you have any additional questions, please contact calnet2-stephelp@berkeley.edu.