Exporting your site from app.colibriwp.com to your own domain is very simple.
Login to your ColibriWP account:
For the selected project, use the Download button, as indicated in the screenshot above.
Clicking that button will prompt you to download the Colibri transfer plugin. All you have to do is install the plugin on a WordPress site on your hosting server and it will automatically transfer your project to that site (including the Colibri builder so you can continue to make changes).