Adding a candidate to a past shift is quite simple. All you need to do is locate the order and navigate to the hired tab.
Locate the past date, click Assign Someone and add the candidate who previously worked the shift.
If for some reason the past shift wasn’t a part of the order and you need to add it, first navigate to the schedule tab and add that shift by hitting the plus sign beside the accurate date. Afterwards, assign the candidate as shared above.