In the past, Facebook made it difficult to undo friend requests that you’ve sent. You had to navigate your settings to block the person in question, and then unblock them; and that’s what most Google results for “how to undo a friend request” will tell you to do.
However, there’s a much easier way. At the bottom-left of their profile, below their list of friends, there’s now a “Cancel friend request” link that, when clicked, does just that! 
