Go to Main Navigation Bar > Meetings > select Meeting>  Attendee (from the Action Menu)

You can add additional attendees to a meeting by hovering over the Attendee button located on the Actions Menu bar of the meeting and clicking Add Attendee.

Complete the required information such as Attendee Name, Attendee Type, Role and Voting,  Permissions, Display and Voting Groups. Once those fields are completed, click on Add Attendee on the top right of the fly out.