Starling 2FA cannot be uninstalled on Password Manager 5.7. There are 3 options:
1) Use your Password Manager Export file to roll back to the configuration before the subscription key was applied.
See the following KB for more information:
2) If the server is a Virtual Machine, revert to a previous snapshot to roll back before the subscription key was applied.
3) Upgrade to Password Manager 5.8 which utilizes the Starling Hybrid Subscription model and has the ability to unjoin. Upgrading will remove Starling.
If you require have questions with regards to upgrading Password Manager please open a support case with the Password Manager product team.