IF! You haven't imported any more images since the one you described. In the library module your folders will show on the left of the screen at the top of the folder list there should be a "previous" import folder. I've not tried this so try it at your risk, see if you can right click on it and delete that import.
However if you have imported other images after the one that created the duplicate images, there's a plugin for LR called something like telesheken that finds duplicate images. OK I found a link to it, my German language skills need a polish [emoji6]
Author: Michael Bungenstock, Category: Software, Name: Teekseelchen, Type: Lightroom Plugin
www.bungenstock.de
Alternatively you could go back to a previous iteration of your Lightroom catalogue dated prior to the date when you created the duplicated catalogue entries. When you open Lightroom under the edit menu at the left side of the menu bar, go to catalogue settings, in there you have the ability to show in explorer where the catalogue is on the disk. At that same location you should find the catalogue backup folders (in date order).
Pick the backup folder prior to when you made the import error. The backup is in a zipped format, you need to extract the zipped file using (extract all) to the same folder.
Then go back to Lightroom, in the library module go to "File" drop down menu and chose open catalogue. Navigate to the folder that contains the unzipped older catalogue and chose that file. Lightroom will give you a prompt advising that it will restart.
When it opens using the older catalogue, check that you are happy with the contents of your catalogue folders, if so go back to the catalogue settings and there's an option in it to create a backup of the catalogue, choose "next time Lightroom is closed". Close that menu then close Lightroom. When you next open Lightroom it should open with the catalog that it backed up when you closed Lightroom.
All of the above is dependent on you creating catalogue backups. I have mine set to create a backup once a week. As I'm not a Pro, once a week is sufficient for the amount of images that I may have imported in a week.
However if I was a Pro, I would set the catalogue to backup every time I quit Lightroom.
IHTH, if you need any help sorting this out send me a PM and we can set up a video call to talk you through the required changes.
