From a Home screen, tap the Phone icon (lower-left).
If unavailable, swipe up from the center of the display then tap Phone.
Tap the Menu icon (upper-right).
Tap the Wi-Fi Calling switch to turn on or off .
If prompted, review the info then tap Turn off Wi-Fi Calling to confirm.
When activating Wi-Fi Calling for the first time, refer to Activate Wi-Fi Calling - Samsung > Activate Wi-Fi Calling via Dialer Setting (Android 9.0) for additional setup instructions.