Simply go in your (Chrome) browser to the Likes-page, e.g. https://twitter.com/{your user handle}/likes
and open the DevTools console (CMD OPT i on a Mac). Paste the following code into the console:
document.querySelectorAll("[data-testid='unlike']").forEach( el => el.click() );
This will click all heart icons on that page, in effect unliking all visible Likes. Scroll down and repeat as many times as needed.