How do you add a button such as the enroll now button to the banner page?
Are you asking about adding the enroll buttons to your course landing page? If so, once your course is published, these will automatically be added to the page.
If that's not what you're looking for, then please send our Support team a little more detail and they'll be happy to help!
How do I remove this button from the banner?
Your best bet would be to transition to our Site Builder themes, as removing the banner is one of the options available to you there.