If you have already backup your data to iCloud before updating your iPhone to iOS 11, then you can easily restore lost iPhone data after iOS 11 update
from iCloud backup.
Here follow the steps to recover lost data from iPhone after iOS 11 updated from iCloud backup:
• On your iPhone go to Settings > General > Reset
and then tap on "Erase all content and settings
• In the Apps & Data
screen, tap on "Restore from iCloud Backup
• Sign in to iCloud with your Apple ID.
• Select the backup from the list of available backups in iCloud to start restore process.
This will start the iCloud Data Recovery process and on completion, you will have all your data back on your iPhone after iOS 11 update.
But in case, if you do not have any backup, then I such case, you have to try iOS 11 Data Recovery
software to retrieve lost or deleted data from iPhone after iOS 11 update.