What program and version do you have and on what computer operating system?
The generalization is that you open the Elements Organizer, select the thumbnails that you want to delete from the Elements Organizer catalog, and then use Delete from Catalog command but do not delete from hard drive save location.
Typically you can select the thumbnail for deletion, right click in the selection, and click on Delete from Catalog from a pop up menu. Or, you can make your selections, and then go to Elements Organizer Edit Menu/Delete Selected Items from Catalog.
Please give more information.
Add On to post 1....
Rethinking your questions...
What you have in the Elements Organizer are copies of the originals that remain at their hard drive save location. So, my first impression of your question was that you were asking about deleting those imports from the Elements Organizer catalog.
But, maybe did you seek information about removing duplicates of imports into the Elements Organizer?
If that is the case, please see the Elements Organizer Find Menu/By Visual Searches, and then
Visually similar photos and videos
Objects appearing in photos
You will need to explore the effectiveness of those choices for what you want to do.