How to click on (x,y) coordinates
You can click on coordinates through context menu.
When you select “Move And Click” action like on screenshot, you will be able to tweak click coordinates through action interface:
If coordinates will be outside viewport border, browser will automatically scroll to desired location.
If you don't want to emulate move event, you can use “Click” instead of “Move And Click” action.
Here is a little hint, how to randomize click location: