2 different movies but considered duplicate of 1 movie how you fix?

Please show the folder structure you are using.
Are all your movies together in the same folder or are you using one subfolder per movie?

Do also look out for .nfo files. If you have those in the same folder with your videos, it can throw off the matching, if it contains an IMDb ID that doesn’t fit the movie.

If your files were previously named differently (and caused mismatches), you need to dance: The Plex Dance ™