A bit of clarification here because this is a mistake I have seen too many make.

The first thing is that You should only use the Plex Series and Plex Movies Agent. They are the official and up-to-date Agents that you need. All other Metadata Agents like TheTVDB and TheMovieDB are outdated and unmaintained. The new Metadata Agents are also faster than the old ones, Unless you use some specific 3rd Party Agents, the Plex Series and plex Movies Agent are more than enough for you because they get their metadata from watch.plex.tv which aggregates them from TheMovieDB, TheTVDB and IMDB.

When you use those agents, you only configure them through the Advanced Section in your library. The “Agents” Section in your Plex Server Settings is absolutely meaningless for those new and official Agents because the Agents listed there are based on the old Metadata Agent system written in Python (IIRC the new ones are written in C++ like the rest of Plex).

Also, that Agent section is based on a Priority list, not on an “override” list. This means that the list is being processed from Top to bottom, each agent in that list will provide their own metadata and write that to the Library item but it will only add metadata that doesn’t already exist yet. This means that if the first metadata agent provides a Synopsis for the library item, the next Agent will not override it.

So, with the new Metadata Agents, there is nothing to override and the Agent section can be completely ignored. Only when you use 3rd party metadata Agents, this section would be of interest to you.

Source: I am the developer of the MyAnimeList Metadata Agent for Plex.