How can I activate the function 'Wi-Fi Calling' in Android 8.1?

To activate/deactivate the function 'Wi-Fi Calling' in Android 8.1, please proceed as follows:

- Open the Phone app
- in the Phone app tap on the three dots in the top right corner to open the menu
- Open Settings
- Open Calling accounts
- Select the provider
- Enable or disable 'Wi-Fi Calling'