In Lightroom, in the Library module, over in the Folders Panel, Click on the + symbol, Select Add folder, navigate to the desired directory/sub-directory (folder), select it. Back in Library module, move the files from wherever they are into the folder you want.
You need to export your selected photos from Lightroom, usually as jpegs, to the desktop or to a new folder/sub-folder. Then add the duplicates to the Photos App.
Select (highlight) the images in the Photos app and if you have already installed the Mimeo extension from the app store simply click the plus icon to the right of My Projects. The Mimeo choice should be listed.