
Apple releases updates once in a while. Users are requested to back up their phone via iCloud or iTunes every time they update their phone to the new version of the OS. There is a minimum chance of users losing their data after an upgrade. If the data is lost after an update, they can restore from iCloud or iTunes as follows.
Step 1
Connect ‘iTunes’
If users had backed up their phone via iTunes before updating to iOS 12, follow the steps below.
- Launch 'iTunes' in computer and ensure if it is updated. Connect iPhone to be restored to the computer via USB
- Click your phone listed in the iTunes after connecting
- Click summary and tap 'Restore Backup'
- Choose the backup that was done before updating. In case the phone was not backed up before updating, choose any old backups and click 'Restore'

Step 2
Connect ‘iCloud’
If the phone is not backed up via iTunes but with iCloud, users can restore it from iCloud. Click ‘Settings’ > ‘General’ > ‘Reset’ > ‘Erase All Content and Settings’.

Step 3
Once the phone is completely erased, click on ‘Apps & Data’, click ‘Restore from iCloud Backup’. Sign-in to iCloud account, click ‘Choose Backup’ and select the latest backup and click ‘Restore’. This would restore your phone completely with the data backed up before iOS12 update.

You have successfully resolved the issue of data loss after iOS 12 update.