The initial page of the application, or the one with the diagram you are working on can become the template document for KinOath Kinship Archiver. To do so:
as for the initial page of the application:File menu > Set Global Default Diagram as (name of the diagram);
as for the page with your project open: File menu > Set Project Default Diagram as (name of the diagram);
File menu > New (default diagram) > the application will open showing the diagram you set as default.
The same thing happens when you close and re-open the application.
To continue working on that diagram you need to recalculate it (see paragraph ???).