Open URL option allows to open diagram exported as URL , insert it into the page and , if necessary, update it using in the editor. The opened diagram will be saved in the page’s attachments.
After you click the Open URL button click, you will see the following dialog will be shown.
After you insert the URL is inserted, and click the Open button click opens a diagram editor setting the uploaded diagram as a source., the diagram will be opened in the editor.
When you have finished working with the diagram, click the Save & Exit button to save the changes and exit editor or Exit to discard the changes made (if any) and leave.
After that, you'll see the preview of the uploaded diagram.