From the left-hand menu, select Manage Participants > Expedition Setup. You can filter the participant by using the 'Location', 'Subgroups' and the 'User details' search box.
Select 'Practice and Qualifying expedition', click 'Practice' for the 'Expedition type' and complete all the fields marked with a red asterisk *. Select the participants you wish to add the practice expedition to and click the 'Add expedition to participants' button on the bottom of the page.
See also the Mapping User Guide attached.