If you have an eSIM and are replacing the existing phone, you will need to download a new eSIM. Now proceed as follows:

Where can I view/change the SIM details?

Log in to your Cockpit and go to SIM --> Settings --> My eSIM Profile:

If the "Transfer eSIM" option is grayed out, the Automatic renewal must be activated. 

The "Load eSIM" or "Switch to eSIM" button cannot be selected

Select the eSIM Transfer option. 

Make sure that your new mobile phone has an internet connection (WLAN) so that you can scan the QR code and download the eSIM. In addition, you must have a second device at hand so that the QR code is visible on it and can be scanned by the mobile phone.