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!
It works very well but at some point facebook shrinks the amount of pages that appear in the activity log upon refreshing. Eventually it says "Nothing to show" even though there's about 600+ pages that are still liked. After waiting I can continue, but I don't know upon what length of time this is based.