How do I tell the Server where to look for files?

Stupidly simple question I can’t figure out. I haven’t used Plex in a long time, and can’t figure out how to tell Plex where to look for files.

Everything looks fine with my library but when I try to play a movie I’m told file is unavailable and I should check to “…make sure the file exists or the necessary drive is mounted”.

I want to make sure Plex is looking in the right location- on an external drive which is mounted and plays fine through quicktime.

I want to double check the file path but I can’t find any sort of preference where to point plex in the web app.

https://support.plex.tv/hc/en-us/articles/200288926-Creating-Libraries

Hover mouse over Library in left pane of Plexweb, click dots, Edit, Add Folders.
There you will see the path to your Library, or if you have no library you can add one because you won’t be able to get that far:

Oh man, thank you. For some reason my external drive unmounts itself and then renames itself with an extra digit on the end as if there were multiple copies.

That will be difficult to use as a Storage Device for Plex. Plex really expects to see the same thing every time. External drives may go missing from time to time - so you would not update those drives or empty trash automatically, but when they do show up they should keep the same name at least - or you’re going to have to add it each time it connects and that’s gonna be a PITA. You’ve probably figured that out though.