Hi! Unfortunately, a number of users have encountered various issues with the latest update.
To resolve your issue, you can try the recovery/DFU mode. This will install the latest iOS version on your device. Note this will erase all the data as well.
Recovery mode:
Turn your device off, then plug it to your computer with the home button pressed. Keep the Home button pressed until you see the iTunes logo on the screen of your device. After that on your computer you should see the iTunes window saying your device needs to be restored to factory settings. Click on the restore button.
More info here:
https://support.apple.com/en-us/HT201263
DFU mode:
- Connect your device to your computer using a USB cable.
- Turn off the device.
- Press and hold the Power button for 3 seconds
- Press the Home button while holding the Power button and hold both for 10 seconds.
- Release the Power button, but KEEP HOLDING the Home button.
- After about 15 seconds, iTunes will tell you it has detected a device in Recovery Mode.
- Restore your device
More info here: https://www.theiphonewiki.com/wiki/DFU_Mode