You can set your mobile phone to select a network automatically or you can select a network manually. If you select a network manually, your mobile phone will lose connection to the network when the selected network is out of range.
Find " SIM settings"
Slide your finger down the display starting from the top edge of your mobile phone.
Press All settings.
Press Network & wireless.
Press Mobile & SIM.
Press SIM settings.
Select one of the following options:
Select a network manually, go to 2a.
Select a network automatically, go to 2b.
2a - Select a network manually
Press Search for networks.
Your mobile phone searches for networks within range.
Press the drop down list below "Select a network".
Press the required network.
Your display will tell you if you have access to the network you've selected.
2b - Select a network automatically
Press Automatic until the function is activated.
Wait while your mobile phone finds the network.
Return to the Home screen
Press the home icon to end the session and return to the Home screen.