How to use this google api console developer tools script for copy clone youtube watch later playlist?

How to use this google api console developer tools script for copy clone youtube watch later playlist? The instructions are old. Now google api console developer tools looks different so i cant find correct way to implement it.

http://www.art4software.com/2014/09/youtube-api-how-to-copy-the-watchlater-list/

Go to Source
Author: Kangarooo