Restore the phone using iTunes.
Installation of updated application Facebook violates working iPhone.
More likely to suffer SE the iPhone and iPhone 6s is that after installation of update regularly crash and spontaneously reboot. In this case, the restart is not performed completely, but only before the appearance of the glowing Apple logo on the screen. Thus, “Apple” smartphones simply turn into “bricks”.
Restore the phone using iTunes from a backup via the USB cable. Read more on the official website of Apple. It will overwrite the data that was on the device.
