to show "Get Started" button in facebook chatbot do the following things.
Click the name of your application and click Channels and Interfaces.
Click a Facebook channel interface.
Click the Behavior tab.
In the Options section, select the Show 'Get Started' button checkbox to display the Get Started button in your chatbot.
But, I am not seeing "Options" section under behavior tab.
Can you confirm that you're using the correct Facebook channel ruleset? you can open it by navigating to Designer Studio > Application definition and then clicking on the rule opener next to the FacebookChannel ruleset.