Losing a login in the authenticator app.

If the account entry was removed from Microsoft Authenticator, there is no undelete option for a single entry.

What can still work:

1. If cloud backup had been enabled before the deletion, try restoring the app backup on the same device type only.
   • Backup and restore must stay on the same platform: iOS-to-iOS or Android-to-Android.
   • On Android, backup is stored with a Microsoft personal account.
   • On iOS, restore depends on iCloud features being enabled.
2. If restoring shows the account with Sign in to restore your account or Action required, open the account in Authenticator and complete the sign-in and additional verification.
3. If Restore from backup or Begin recovery does not appear, sign out of or remove all accounts in Authenticator first, then start the restore flow before signing in.
4. If no backup exists, or the backup was overwritten after the deletion, the removed Roblox TOTP entry cannot be recovered from Authenticator. The account must be added again through Roblox account recovery or by resetting two-step verification on that service.

What is restored:

• Third-party accounts such as Roblox use one-time password codes, and those codes are available after restore if they were included in the backup.
• Work or school accounts restore only the account name and require sign-in again.
• Microsoft personal accounts with passwordless sign-in restore only the account name and require sign-in again.

If access to the backup account is also lost, support agents cannot restore the Authenticator backup. In that case, the only path is to regain access to the backup account or re-add the affected accounts individually.

References:

• Back up your accounts in Microsoft Authenticator
• Restore account credentials from Microsoft Authenticator
• Accidentally removed account from authentication app - Microsoft Q&A