The easiest way to register a new mobile device to an existing Avira account is to install the app on the new mobile.
To do so, launch Google Play on your mobile device, download the Avira Antivirus Security app and install it on your device.
If your installation has been successful, continue with the registration. During registration, you must use the same email account that you have used for the other device.
In your Avira account, the new device is displayed on the dashboard.