From their profile
Open the person's profile and click the Requested button. The request is withdrawn.
From Connections
Open Connections in the side menu and go to Requests.
Switch the selector from Pending to Sent — that's the list of requests waiting on other people.
Cancel the request beside the person's name.
One thing to know
Sending a friend request also followed them. Cancelling the request doesn't undo that — you'll still be following, and their posts will still appear in your feed. Unfollow separately if you'd rather not: see Unfollowing Someone Without Unfriending Them.
The person isn't told that you cancelled.
Need help? Contact support at [email protected]