On Android smartphone:
- Go to Settings;
- Choose Mobile Networks (if your device is running Android Lollipop, you will need to choose More Networks, then Mobile Networks);
- Choose Network Operators;
- Disable Automatic search and choose the required network from the list.
On iOS devices:
- Press Settings;
- Select Celluar/Cellular plan
- Choose Network Selection;
- To select the network manually, press the indicator next to Automatic until the function is deactivated;
- You will see a list of the network operators available. Click on the required network.