I've gotten myself in something of a mess with installing a new library.
I installed the library .ZIP file fine, but unfortunately the wrong files were in the .ZIP file so it generated up a bunch of error messages. I couldn't see a way to delete or update a contributed library from the library manager, so I just deleted this library sub-folder in the arduino/libraries folder.
I assumed that when the IDE loaded again it looked at the arduino/libraries folder to see what libraries were included and, not finding the folder, it wouldn't show up on the list of contributed libraries. It appears I was wrong. It's still showing the contributed library that I deleted. When I try to reload the library (this time with the correct files in the .ZIP file), it tells me that the library is already present, so it won't reload it.
In the Library manager it's just listed as "unknown version INSTALLED" with no update or delete option.
Question: How do I tell IDE or library manager that the contributed library it thinks is there isn't there so I can install the correct version (with the same name). How do I fully remove that library so that I can start again?