Go to: https://m.facebook.com/pages/launchpoint/liked_pages
Paste the following script into console (F12 -> console):
var unlike_all = ()=> {
[].slice.call(document.querySelectorAll('[data-sigil="action-title"')).filter(x=>x.innerText.indexOf('Unlike') !=-1).map(x=>{x.click()});
window.scrollTo(0,document.body.scrollHeight);
window.setTimeout(unlike_all, 3 * 1000)
};
unlike_all();
you're done!
would be more powerful if worked on the activity log of liked pages to avoid being blocked
https://www.facebook.com/usrID/allactivity?activity_history=false&category_key=LIKEDINTERESTS&manage_mode=false&should_load_landing_page=false