just download the file via the amazon link below the screenshots and paste it into the folder where all the other sanctums are located (same folder as the valentine and gleambow ones)
EDIT: this is the path it gave me: C:\Program Files (x86)\Steam\steamapps\common\Boundless\assets\sanctum
Then just go to your sanctum in game> hit f1> sanctum editor > load > marble sanctum.dat
followed by ‘return to game with this sanctum’ in the sanctum editor pop up
Once in sanctum press f1, this brings up the debug menu.
Then use mouse to select edit sanctum and if I remember there should be instructions there press f1 to leave debug menu to regain control of in game character.