1. Create a backup of the iphone with your Windows or Apple computer (Mac) (not on icloud). The backup must be encrypted.
2. Recover the backup file
On macOS, iTunes will store backups in /Users/[USERNAME]/Library/Application Support/MobileSync/Backup . (macOS 10.15 creates backups using the Finder rather than iTunes, but these backups are stored in the same location)
On Windows Vista, Windows 7, 8 and Windows 10, iTunes will store the backups in \Users\[USERNAME]\AppData\Roaming\Apple Computer\MobileSync\Backup.
3 Transmit it to us by ftp, drive, dropbox… etc. Caution it will be a big file. If needed we can open a dedicated account on one of our servers