See: wwww facebook com | Facebook Login | Facebook Log In Facebook
Turn on your Android phone
Tap the Menu button to go to the apps list.
Locate and tap the Facebook icon.
If you are not already logged-in, provide your credentials in the appropriate fields, and tap the Log In button.
Once the News Feed page opens up, tap the Search icon (icon with magnifying glass symbol) in the title bar.
Once done, enter the name of the user in the search box whom you have sent the Facebook friend request accidentally.
Once the user is found, tap the user’s name to go to his/her timeline.
On the open interface, tap the Friend Request Sent button.
From the displayed options, tap the Cancel Request button to cancel the friend request.