You can change your attendance status simply by choosing IN, MAYBE, or OUT if you’re a registered attendee for the event. If the team, organization, or league is a PREMIUM member and you have a mobile phone registered to your profile - you can also simply reply Y, N, or M to the text message sent to your phone.
If your event supports SPARES and you are a spare, you can check-in for the event and you’ll be marked as WAITLIST. Only the team manager or event manager can then change your status for the event and you’ll be notified.