This is the screen you will see on the Door Tablet application just before you check-in to a meeting space:
Once you have checked-in, the options at the bottom right of the screen will change. You will see these options instead:
Click on "Extend Booking". Note: you can only extend the meeting once and the duration is determined in the meeting space settings or the remaining time until the next meeting, whichever is sooner. The following message will pop up:
Please enter the Check-in Code that you were given and press "OK".
You have now extended the meeting.