How can I edit the collections?

I have about 20 “collections” that seem to have been automatically added (but are not very useful - ie when I added the last Hunger Games movie, it created a Hunger Games collection, but did not add the other Hunger Games movies!).

What I want to do is create a “Christmas Move” collection, but the list is so junked up with automatically created collection names, that it’s making it cumbersome. So:

How do I edit the collections (I read somewhere about editing the database file, directly - I do NOT want to risk mucking up my data file, this should be possible in the software)? I want to basically go in and remove about 20 existing and useless collections.

I want to edit the collection - I want to be able to say “add movies” to a collection and then find the movies I want, not go searching for movies and then add them to the collection. I know this seems trivial, but when you have a bunch of collections (see earlier question) this is a much faster process.

How do I keep PLEX from automatically creating these useless collections in the future?

Thanks!