There are no "buttons" in Numbers to which an automator app or Applescript can be assigned. You can assign a key combination, though, if you make your automator document a "quick action" so it shows up in the Numbers/Services menu. "Run AppleScript" is one of the actions in Automator so you can also assign a key combo to an AppleScript.
If you need a "button", you could try making an app in Automator and then placing that app in the dock where you can click on it. For instance, I created a very simple app to do the key combination for "full screen" (which is the same across a lot of Apple apps) and I placed it in the dock so I could invoke it with a click when running apps I want to see in full screen (like for watching movies in Quicktime).
Watch me do is pretty limited in what it can do. If you need to click on a cell in a table, that cell better be in the same X-Y location in the window as it was when you recorded the "watch me do" or it will click in the wrong cell or not in the table at all.