One site with an established track record of helping people out of false conspiracy theory rabbit holes is metabunk.org. They have mainly helped people with 9/11, chemtrails, and UFOs. The guy who runs the site has written a good book on it:
https://www.metabunk.org/threads/escaping-the-rabbit-hole-bo...
Read an excerpt at https://www.salon.com/2018/09/16/how-to-pull-a-friend-out-of...
It is the best resource I have found in many years of searching but if you can suggest others, please do so.