Drag the folder with your files into the program window of this app.
Check if the files are tagged with an “Album Artist” tag. (This is not the regular “Artist” tag!)
Do also look for the “disc #” tag and set it, if missing.
Once you’ve done the above, remove the part “[Disc n]” from the album title meta tag. It doesn’t belong in there.
(Side note: the underscore is just a stylization on the album cover. You should use the album title as it is listed on Musicbrainz Prince - MusicBrainz )
Organize the files in a folder structure like this: https://support.plex.tv/articles/200265296-adding-music-media-from-folders/
Once you’ve done all that, perform the Plex dance with the album.
