Only MSL can access the Clear Duplicates field. When clicked, this action clears the list of Duplicates. The list will be repopulated overnight when the automatic import process runs. It's advisable to use this feature periodically to refresh the list, as there may be entries in the Duplicates list that haven't appeared in the main import data for some time. Removing them helps clarify the situation.
For further information, see Duplicates.