Some additional information:
Not sure what steps you took to add the new version.
However, next time you replace an existing movie, add the new version first, without deleting the original. After Plex picks up the new version, then delete the original.
This keep Plex from having to completely re-recognize the movie, download metadata, etc. You’ll also keep played/unplayed status, etc.
If it does not work for some reason, you can always perform the Plex Dance. However, the movie will reappear as a new addition to your system, you lose played/unplayed status for your users, etc.
Example:
You have an existing movie: /Movies/Avatar (2009)/Avatar (2009).mkv
Add the new version to the same directory (*). Add some info to make the file names different.
/Movies/Avatar (2009)/Avatar (2009).mkv
/Movies/Avatar (2009)/Avatar (2009) [1080p].mkv
If Plex does not scan the library automatically, perform a manual scan to pick up the new movie. Plex should recognize both versions (**). You’ll see a “2” in the corner of the cover art.
Now delete the original version of the movie (or just move it to where Plex cannot see it).
Then scan the library, empty trash, and clean bundles.
(*) You can use separate directories if desired, as long as both are added to the same library.
(**) Plex may not always combine the movies when you add the second version. They may both appear as individual movies in the library.
If this happens, first rescan the library again. Plex sometimes combines things with a second scan.
If that does not work, then perform a Fix Match. You may have to perform it on both versions of the movie.
To perform a Fix Match, move your mouse over the cover art. Click on the three vertical dots in the lower right corner and choose Fix Match. Fill in the appropriate information, click search, and pick the correct match. Plex should then combine the movies, showing the “2” in the upper left corner.
