I don’t think it’s possible to do a global “unlike” on FB. Though you might try going to G**gle and typing in “how to unlike all likes on Facebook” or something along those lines. I’m always astounded at how many people have taken the time to post every single thing they ever thought about on the Internet. Maybe you’ll hit gold.
The only thing I’d hit is a brick wall. It is not my custom to frequent - how should we say - unsecured search engines.