Follow the instructions below on how to delete participants.
Click Workplan in Home menu, this will open the "Workplan" section.
Click the quick action menu at the participant that you would like to delete and choose Delete.
Note: If any resource entries are associated with this participant, first you must unlink these resources from the participant. Hover over an affected entry and click the "Edit" icon to open and update the entry in the sidebar:
To delete the participant, click Yes in the appeared window.