Many iphone users have complained to have faced the problem of red screen while rebooting the phone, after an update to iOS 11 or after screen replacement, water damage. Here are some ways we can resolve this issue:
Restart your iphone.
Firstly, you can try the easiest and most convenient option, restart your iphone and check if the phone starts without any red screen problem.
Put your iPhone in DFU Mode.
If the iPhone still shows red screen, blue screen, boot loop after restarting the phone, next try to put your iPhone into DFU mode and restore
the iPhone with iTunes. To get rid of the current firmware, use DFU mode with iTunes to restore your handset. Follow the below steps to enter DFU mode of your iphone6
Connect your iPhone 6 to the PC via USB cable and check if iTunes is running.
Turn off your iPhone 6 by holding down the "Power" button and then slide to power off confirmation to the right.
Press and Hold the "HOME" button and the "POWER" button at the same time for atleast 10 seconds, and release the power button but keep holding "HOME" button.
If you see the "Plug into iTunes" screen then you have held it too long and you will need to start again.
If the screen is black, your iPhone 6 should now be in DFU mode.
Hard Reset iphone
To hard reset the phone, press and hold the Home
button simultaneously until you see the Apple logo appear on the screen.
Before fixing iphone issue, backup your data as data might get deleted in the process.