This can be done by going to Register > Manage Register. In this area enter the date of the day you wish to record/edit the late pickups for and any options for year or form that you require.
Then check the box to Manage Late Pickups for (date) and click View Register. You can then enter a note and time for the late pick up.
Please note that you can only manage late pickups for one day at a time.
Top Tip: You can report on late pickups in Reporting > Reports > Attendance (tab) > Late Pickups.