Step 1) Try your iTunes Store password first. This is most commonly the password to restore your backup. Step 2) Try your 4 digit unlock code for your device.
How to restore iPhone from iTunes backup after downgrade:
Let the update finish, and wait for your device to restart. Erase your device: Tap Settings > General > Transfer or Reset [device] > Erase All Content and Settings. After your device is erased, it restarts and you'll see the Hello screen in the Setup Assistant.
Backup your iPhone 7 Plus via iCloud
If your iPhone apps still say waiting after iTunes restore, you can restart it to turn off unknown background programs and release temporary memory caches. Restart iPhone: Hold Sleep/Wake button > Slide to Power off >Hold Sleep/Wake button again.
Although Apple recommends creating a backup of your iPhone before installing iOS updates, you can install the latest system updates for your phone without a backup. Backing up your system is not a mandatory prerequisite for installing iOS updates.
Restore iPhone 7 using iTunes:
Restore iPad from a computer backup Do one of the following: In the Finder sidebar on your Mac: Select your iPad, then click Trust. To use the Finder to restore iPad from a backup, macOS 10.15 or later is required. With earlier versions of macOS, use iTunes to restore from a backup.
Restore all content to iPhone from a backup
Click the devices icon and then click “Restore Backup” under the Backups menu. Step 3. Select the latest iTunes backup according to the iPhone name in the popup window and click “Restore”. Wait for the iTunes backup restore process to complete, and you will get all your contacts back.
Step 1: Connect your iPhone and Mac or PC using a USB cable. Step 2: Tap 'Trust This Computer' on the iPhone. Step 3: Launch DearMob iPhone Manager and click 'Backup'. Step 4: Click on 'Backup Now'.
Part 2: Restore iPhone backup without iTunes