To unlock the bootloader switch of the phone. Then boot into bootloader/fastboot mode by holding volume down + power.
Plug the phone to your computer and make sure it could be found:
cd C:\Users\idefix\AppData\Local\Android\Sdk\platform-tools fastboot devices
If it is found, continue:
fastboot oem unlock
Confirm on the phone using the volumn key and power button.
Reboot the phone with:
Now wait till the phone is completely booted again and restore your backup.