From within a browser go to: https://twitter.com/{username}/likes
Open the console and run the following JavaScript code:
setInterval(() => { for (const d of document.querySelectorAll('div[data-testid="unlike"]')) { d.click() } window.scrollTo(0, document.body.scrollHeight) }, 1000)
Might take a while to run if you have a lot of likes. Took me about 5 minutes to delete 2k likes.