Rewind lets you take back your last swipe. If you accidentally swiped left on someone you wanted to get to know, they are no longer lost in the Tindersphere forever. Use Rewind to bring their profile back and swipe again, just tap the yellow arrow icon on the main screen.
Only Tinder Plus and Tinder Gold users can rewind a swipe, and they can only rewind their last swipe.
To subscribe, tap the profile icon at the top of the main page > Settings > Get Tinder Plus or Get Tinder Gold.