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 two fingers downwards starting from the top of the screen.
Press the settings icon.
Press SIM card & mobile data.
Press the required SIM.
Press the indicator below "SIM Info & Settings" to turn use of the SIM on or off.
Press the Return key.
Press the required setting.
Press Mobile data.
Press the Home key to return to the home screen.