Here's how to reset all of your iPhone 6s' settings:
- From the Home screen, select Settings.
- Select General.
- Restart by pressing the Reset button.
- Choose Reset All Settings from the drop-down menu.
- To continue, enter the passcode if required.
All of your preferences will be reset to factory defaults after that. Resetting all of your iPhone's settings may also be the best way to fix No Camera Flash And Focus issues caused by software flaws or corrupted material.