Hello,
Thank you very much for choosing our theme and for contacting us.
You need to find or create a Maintenance page, this page can have any content you wish, however you need to set “maintenance template” in the page settings: https://gyazo.com/5c81e8a0e2d502726283d118bad0cba7
So, you need to enable the mode in the Theme Settings and set the page for the mode and it would work.
If you have uploaded the demo there are three Maintenance mode page templates, you can edit them as any common page and set the appropriate template.
If you have any questions please feel free to contact us.
Best Regards