How to add an object to a button in Unity

So I was following a tutorial for Flappy Bird, and at some point I wrote a script for the play button but the button object in the heirarchy didn’t have any where to put my script

I tried looking at youtube videos but most guides were even before this one was made so I knew that they wouldn’t help. In the component for the button it has the “On Click” option but no handler to put the script/object in. Because I can’t find an updated guide for the button does anyone else know where I would use it?