To sign-in with authenticator app two-factor method, first enter your username and password and click Sign in.
Then, open authenticator app on your device, and get the 6-digit code next to your Zammad account.
Back in Zammad, enter the provided code to the Security Code field and click on Sign in.
Warning
Entering security codes from your authenticator app is a time-sensitive operation! Each code is valid for up to 30 seconds, so if you are near the end of the time window (timer will show you this), it is better to wait for it to refresh.