If Expired badges are shown in the bottom right of the main window, you can click on the button to give you a list of all the expired badges.
Here you can select one or more visitors and either check them out if you know that they have left, or select a time period to extend they stay by.
Some details are also shown for the invitee so that you can try to contact them if needed.
Once you are done click on Apply to save the changes.
