Apple iPad Pro 12.9 (2018)
iOS 12.1
1 Find "Mobile Data Options"
Press Settings.
Press Mobile Data.
Press Mobile Data Options.
2 Turn data roaming on or off
Press the indicator next to "Data Roaming" to turn the function on or off.
3 Return to the home screen
Slide your finger upwards starting from the bottom of the screen to return to the home screen.