Go to Assessments > Dispatches. Deselect the My dispatches checkbox on the top left of the table if you have the Assessment Administrator permission and want to see dispatches created by another user. Point to an assessment and click the 3-dot icon on the right side of the page. Select Add Participants.
A dispatch is marked as complete once all participants have submitted the assessment. If you're the dispatch creator or if you have the Assessment Administrator permission, you can reopen the dispatch to add participants.
Go to Dispatches and select Completed in the Status filter. Deselect the My dispatches checkbox if you're looking for a dispatch created by someone else. Point to the assessment and click the 3-dot icon . Select Reopen and click OK to confirm.