after reset my mobile authenticator is not working

Restore Authenticator from its cloud backup if one existed before the reset; otherwise, replace the personal Microsoft account’s security information and wait 30 days before signing in.

1. Restore Authenticator if backup was enabled

Restoration must use the same device type as the original backup—Android to Android or iPhone to iPhone. For personal Microsoft accounts, backed-up 30-second one-time codes can be restored, but passwordless credentials require signing in again.^1^

Android

1. Open Microsoft Authenticator.
2. Before signing into the app, select Restore from backup or Begin recovery.
3. Sign in with the personal Microsoft account used to create the backup.
4. Select the restored account and complete any Action required prompt.

If the restore option is missing, sign out of or remove accounts currently added to Authenticator, reopen it, and select Restore from backup.

iPhone

1. Confirm that the phone uses the same Apple/iCloud account used for the backup.
2. Install and open Microsoft Authenticator.
3. The backed-up accounts and eligible codes should appear.
4. For an account showing Sign in to restore your account, select Sign in and complete the requested verification.

2. If there was no backup

A factory reset removes the Authenticator registration stored on the phone. Reinstalling the app cannot recreate its codes without either a previous cloud backup or access to the account so that Authenticator can be registered again.^2^

Because Authenticator is your only verification method:

1. Start signing in to your Microsoft account.
2. At Verify your identity, look for I don’t have any of these.
3. Follow the prompts to replace your security information with a new accessible email address or mobile number.
4. After submitting the replacement, Microsoft requires a 30-day waiting period before you can sign in with the new security information.^3^
5. After access is restored, open the account’s advanced security settings, remove the old Authenticator registration, and add Authenticator again by scanning the new QR code.

The 30-day period cannot be bypassed by support. If you recover access to the original Authenticator information during that period and use it to sign in, the security-information replacement will be cancelled.

Important limitation

If two-step verification was enabled, there was no Authenticator backup, and the sign-in page provides neither an alternate method nor I don’t have any of these, the standard recovery form cannot bypass two-step verification. Microsoft support agents cannot send a reset link or manually change the account’s verification details.^4^

Do not repeatedly request codes; repeated attempts can trigger a temporary block.^3^

References

1. iOS
2. Accidentally Factory Reseted my phone - Microsoft Q&A
3. Troubleshoot Microsoft verification code issues | Microsoft Support
4. Help with the Microsoft account recovery form | Microsoft Support