If for any reason you experience issues with the 2FA authenticator, the option to recover access is available on the page, after the initial screen of username+password:
You need to click on Recuperer/Recover (the language can be adapted to the one prefered by the user)
You will be prompted that a code is sent to your recovery email. This can take several minutes. you should wait until the email reception (and check spam/junk, as well, before hitting the Cliquez ici/Click here button, in case the email does not arrive):
Once the email recovery code is received, this page opens up. You should not type in the code you already received. What you needs to do is either use a QR reader and scan the visible code to get the authenticator code or hit the unable to scan button and the code/key will be written so that it can be copied/pasted (particularly useful for desktop authenticators):
The code/key mentioned above will look like this:
This key needs to be typed in a mobile/desktop authenticator, as seen below (the one used is just one of the many available, but they all mostly work in the same way):
Once you hit the Add account button you will be prompted to give the authenticator a name (Adminbox, for example) or you can just keep the date as the name, this is not really important for the way the authenticator works, and afterwards you will get a changeable code that needs to be used for each login, after they input their username and password:
This same code needs to be typed in at this step of the 2FA recovery:
Then you can hit the Continuer/Continue button and you should be logged into their account.