Press the Add Members button (button icon is a rounded square with a “plus” symbol) in the reference set summary section to add all distinct members of the comparison reference set to the active (selected) reference set.
OR
Select Comparison Reference Set from the Reference Set Membership dropdown list to populate the table with members only in the comparison reference set; AND
Press the Add Member button (button icon is a rounded square with a “plus” symbol) to the left of any member to add it to the active (selected) reference set.
NOTE: An author may add or remove members from the selected (active) reference set only when it is in “In Edit” workflow status when the comparison is launched.