See Why is some of my content not found?
Make sure you follow Plex naming & organization requirements.
Plex Dance the movie after renaming / reorganizing.
Plex Documentation → Your Media
→ Naming & Organizing Your TV Show Files
→ Naming & Organizing Your Movie Files
If you need to rename many files:
Many people use Filebot. It is quite powerful and can rename an entire library in minutes.
Tiny Media Manager is also very useful, and free.
TMM Renamer Patterns:
- Show Name:
${showTitle} (${showYear}) - Season:
Season ${seasonNr2} - Episode Name:
${showTitle} (${showYear}) s${seasonNr2}e${episodeNr2} ${episode.title} - Movie Name:
${title} (${year}) {imdb-${imdb}}
PowerRenamer in Microsoft Power Tools is helpful for simple renaming with pattern matches or regular expressions. It makes quick work of tasks such as adding a year to file names, removing undesirable text from multiple files, etc