Welcome to the Apple Community.
Is that 3.5 GB a back up, if so.......
Navigate to Settings > General > Reset > Erase all contents and settings on the device you want to restore.
When this completes and the Set-Up Assistant starts, choose "Restore from iCloud Backup" and enter your iCloud account and password. You will see the three most recent backups for each of the devices on which you enabled Backup. Choose which backup to restore from.