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.
Slide your finger downwards starting from the top of the screen.
Press the settings icon.
Press SIM card & mobile data.
Press the required SIM.
Press the indicator next to "Enable" to turn use of the SIM on or off.
Press the Return key.
Press the required setting.
If you change SIM, press Switch.
Press the Home key to return to the home screen.