Even with an old Configurator, you generally cannot downgrade a device's iOS version unless Apple is still "signing" that specific firmware. Experts Exchange
The most reliable way to get an Apple Configurator old version is to have a Time Machine backup from the era when it was installed. apple configurator old version
may host DMG files, these are not official and can contain malware. IPSW Limitations: Even with an old Configurator, you generally cannot