Samsung Galaxy A3 (2016)
Android 5.1.1
1 Find "Network operators"
Slide your finger downwards starting from the top of the screen.
Press the settings icon.
Press Mobile networks.
Press Network operators.
2 Select network
Press Search networks and your phone will search for networks.
Press the required network.
If you want to select a network automatically, press Select automatically.
3 Return to the home screen
Press the Home key to return to the home screen.