If you are using the Diary or Floor plan view to check people in, you'll need to bring up the left-hand side check in panel by clicking the people icon at the top of your grid view.
> then click on the booking to bring up an expanded panel to the right with more booking details
> you will see that there is a ‘Check in’ section with three boxes (as below), the field to the left shows the number of covers the booking has been made for, the second is your 'No Show' button and the third box is to enter in the actual number of guests that arrived
> to un-check the booking - select 'Uncheck Guest' from the drop-down menu in the third 'Actua Guests' box
If using the interactive Run sheet view, once you've checked in the booking, the Guests field will display the Guests vs Actual Guests - see screenshot below.
Click on this to bring up a drop down list to change the 'actual guest' amount/ or to 'Uncheck Guest'