Change the index from Root directory to something else

Okay I know this topic has been brought up countless times, but I can’t seem to find how to go about it in the opposite direction.

I’ve got all my wordpress files and index page in my root directory, how I want to move all of that into a sub-directory.

Seems most of the conversations (including the docs page) show how to go in the opposite direction. Can anyone remember/find the relevant thread? I’m sure countless others have asked this.Thanks guys.