Let’s start over:
Do you want
- the two files look and play like one long movie
- the two files look like 2 movies, so your users can easily pick which part to watch
The latter is what is described in the above link.
The former requires a certain way to name the files, which is described in here:
https://support.plex.tv/articles/200264966-naming-multi-file-movies/
If the 2 parts are coded exactly the same way, you can also try to merge them into one common file. Which is what I would try to do, since it is the cleanest solution:
