Thanks for writing in!
I checked the website and can see that Cornerstone is not installed yet. Please visit X menu in the backend to automatically install Cornerstone. Once you visit X menu, you will see the option to Validate Theme. More information on validation here:
After theme is validated, you can see the option to import the demo content under X > Validation > Demo Content.
In case you face any issues, please share website login details in secure note for us to take a closer look.