After you added an account in your authenticator application you don't need to scan QR code again. All you have to do is:
Step 1. Log in with your credentials (username and password) as usual. The second-factor authentication page will open.
Now you have 3 options:
1 Option. Plug your U2F device in, click Submit, and press the button on the device.
2 Option. In case you don't have your U2F device you can use your mobile authenticator app. Click Enter a two-factor code from your phone. Find out How to log in using your phone here.
3 Option. In case you have neither U2F device nor mobile authenticator (phone) you can use backup (recovery) codes and enter a one-time secret reserve key.
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