You can add guests directly from the check-in app during an event.
How to Add a Guest
Select the Guest list tab at the top of the screen.
Tap Add guest in the toolbar.
Enter the guest's name.
Select an existing tag from the dropdown, or type a new tag name.
Optionally adjust the Plus ones stepper to add unnamed additional guests.
Tap Add guest to save.
To add further details such as email, guest notes, or manage tags, tap the guest's name in the guest list to open their profile.
