You can only cancel a sent friend request on the website; this feature is not available in the app.
If you have too many pending friend requests and can't send any more, follow these steps to cancel them:
Hover over Social in the left menu, then click Friends:
On the Friends page, find the Friend Requests menu on the right side of the screen. Here, you can manage both incoming and outgoing requests.
Click on Outgoing to see the requests you've sent.
Click the X next to a request to cancel it:
