The Submitter (not co-presenter) can edit submission.
To edit submission, log into the ABC site and click My Profile, then click My Options. Next, select My Presentations (at bottom of list—lower right corner). Click your San Diego submission.
From the submission, find pencil icon on left. After clicking the pencil, edit as desired. (You will find co-author section by scrolling down past the long list of co-presenters.) Go to bottom and press OK when done.