If you accidentally (or even if you intentionally) checked in a guest and need to undo that. You can "un-check-in" a guest in the Auction manager.
Simply go to the guest list (Left Menu -> People -> Guests -> Guest List)
- Find the guest or guests that you want to "un-check-in".
- Click the check box next to each of their names
- Tap the "Un-Check-in" icon at the top of the screen
- Confirm that you want to do this by clicking on "CONFIRM" in the confirmation screen