When you insert two SIMs into your phone, you can make calls and send and receive messages from both SIMs. You can also select a default SIM for mobile data usage.
Press Wireless & networks.
Press Dual SIM settings.
Press the indicator next to the required SIM to turn use of the SIM on or off.
Press the field next to “Default mobile data” below the required SIM.
Press Default calling SIM.
Press the required setting.
Press the Home key to return to the home screen.