Samsung Galaxy S8
Android 7.0
Select help topic
1. Find "Wi-Fi"
Slide your finger downwards starting from the top of the screen.
Press the settings icon.
Press Connections.
Press Wi-Fi.
2. Turn automatic use of mobile data on or off
Press ADVANCED.
Press the indicator next to "Smart network switch" to turn the function on or off.
3. Return to the home screen
Press the Home key to return to the home screen.