To see the list to be exported, a sub summary part can be used for this.
- Define a sub summary part "when sorted by" the field that contains duplicates.
- Delete the body part from this layout by clicking on the Body part label while in layout mode and press the delete key.
Whether you create such a layout or not, you can sort your records by this field and use export records with the Group By (select this same field) option selected to get one record per group exported.
Thanks, PhilModJunk, that did the trick!