You can get the vanilla Options button back via the editor menu. Open the layout where the button disappeared, then go to the menu bar → Element → Deleted Vanilla Elements and left-click the “Options” entry to make it visible again.
Vanilla buttons don’t expose their action scripts, so you can’t edit what they do there—if you want a custom button with your own actions, add a new custom button and assign it actions via Edit Action Script instead.
More detail is on the Deleted Vanilla Elements page.