I remember the first time I needed to return a Kindle Unlimited book, and it took me a minute to figure it out. You have to go to your 'Content and Devices' page on Amazon. Just log in to your Amazon account, hover over 'Account & Lists' at the top right, and click 'Content and Devices.' From there, select the 'Books' tab, find the Kindle Unlimited book you want to return, and click the 'Return this book' button next to it. It’s pretty straightforward once you know where to look. I’ve returned a few books this way when they didn’t grab my attention after the first few chapters. The process is quick, and you can borrow another book right away.
Sometimes, if you’re using the Kindle app, you might not see the return option immediately. In that case, try accessing the website directly. I’ve noticed the mobile site sometimes hides options, so switching to desktop view helps. Also, keep in mind that returning a book frees up your slot for a new one, which is great because Kindle Unlimited has so many hidden gems waiting to be discovered.