1. First, turn your mobile phone off by pressing Power key.
2. Next, hold down Volume Down + Power key.
3. After the device vibrates, release Volume Down and press Volume Up.
4. If you did it right, the phone will vibrate again. When it happens, release all the buttons.
5. Good job! You should now be in the desired mode.
6. Now you can navigate the mode by using the Volume buttons and confirm options by holding the Power key.