In order to find Facebook friend-requests that you previously received, but chose to postpone at the time using the Not Now option, you should:
- Click on the Friend Requests icon on the top menu-bar. A menu will open.
- Click on See All at the bottom of that menu.
There, you will see all of your previously-received friend-requests. For each one, you can click on Confirm or Delete Request, if you wish.
Facebook does not offer a way for you to see friend-requests that you previously rejected explicitly or deleted