Manual unpack of PSA backup file

PSA backup files is actually .zip files. Just rename it to "filename.zip" instead of "filename.psa"

Renamed the folder "D:\Parallels\Plesk\Backups" to "D:\Parallels\Plesk\Backups.old" to save any old backups.

Copy the content of the needed backup archive to new "Backups" folder.
Then refreshed the information in Plesk Backup Manager by clicking "refresh".
Now the backup is available from Plesk GUI.