You are able to either add all attendees manually or import a list into your event. Once you navigate to the Attendee Tab, you can either click + Add or ^Upload.
You are able to import a .CSV or .XLS file under the Attendees tab. Once you click upload and select your file, you are able to map the correct columns in your file into the Event Fields.
You are also able to invite all of your previous attendees to your new event by clicking Add Attendees from Other Event. This will allow you to select a few or all attendees, and add them to your new event.
How to Add Attendees to Your Event: