Create a new map in Kumu, open up the javascript console, and point the map at the blueprint:
Workflows.setCurrentMapSource("https://example.com/path/to/blueprint.json");
For example, if you wanted to load the blueprint below you would use
Workflows.setCurrentMapSource("https://gist.githubusercontent.com/rymohr/06533f749645f13c7732/raw/420f21f74b6de68485347af058f1a3f8b12b89a9/simple-kumu-blueprint.json");