1
Navigate to the "Crowds" tab.
2
Enter the Crowd you wish to add the existing member to.
3
At the top right you will see the "Add Member(s)" button.
4
A popup window will appear for adding existing participants to this Crowd. Click the checkbox(es) of the participant(s) you wish to add.
5
Then click the "Add" button on the bottom right of the popup, and those members will be added to the crowd.
6
You can also use the share functionality as an alternate way of adding existing members, allowing them to join via that share link.