During the event application, after the registration form, you will be prompted to enter your team's blackout dates for that event (assuming the event has this option activated).
First you will click into the date field to add your first date:
After you enter your first date, click Add Additional Date to add another date as needed (each event can set a limit on how many blackout dates may be entered, so this will vary by event):
When you are finished entering your blackout dates, click Save and Continue to move to the next page of the event registration: