To sync your Calendar with Eventbrite take those actions:
Click on the Calendar and open the Settings.
Click on the Add-ons section.
Open Add-ons Store.
After adding to your site, connect Eventbrite.
After clicking on Connect, sign in or sign up Eventbrite and with the next step click on "Allow" to connect your Eventbrite with Calendar.
To finalize your actions, enable synchronization, and choose sync method Auto or Manual. If you want your events to be populated automatically your can choose Auto option. Or you can choose Manual option and choose the events that will appear on the Calendar.
All the events that are auto synced from the external calendar are not available in our Calendar settings. So, you should modify your synced events only in Eventbrite Calendar settings.