Plex Documentation → Your Media → Naming & Organizing Your TV Show Files
Make sure you are using Plex recommended naming and organization.
You can pick aired, dvd, or absolute episode ordering from TheTVDB.com or aired ordering from themoviedb.org. See screenshots below.
You may need to Plex Dance the show after reorganizing / renaming.
/TV Shows <-- folder added to TV Show library
../Show Name (year) {tvdb-zzzzz} <-- year = show's first year. tvdb/tmdb ID is optional, but assists with matching.
..../Season xx <-- "Season" in English. Two digits for number, unless four required.
....../Show Name (year) - sXXeYY - optional episode name.ext <-- ext = mp4/mkv/etc.


Selecting Aired / DVD / Absolute Ordering
You can organize your files using either the Aired (default), DVD or Absolute order. In Plex, edit the show (not season or episode), select advanced, pick preferred organization.