You receive the following message when trying to restore a backup onto an iPhone:

Find my iPhone must be turned off before "phone_name" can be restored.

Go to iCloud Settings on your iPhone and turn off Find My iPhone before restoring your iPhone.

You cannot restore an iPhone from backup if Find My iPhone is enabled.

Go to Settings > iCloud, and disable Find My iPhone. Then, try to restore the backup onto the phone again.

If the iPhone's software is not functioning in such a way that you are prevented from getting into the Settings, then try a DFU restore.