Blueprint for specific group of images on subpage

Hi everyone,
im trying to figure out how to create a blueprint for a specific group of images that are on a subpage. where should the blueprint be stored? how do I name it? And specially how do I link it just to the images of my subpage without creating problems with the default.yml for all other images/files?

Up to you

By setting it to the section/field through which you upload the file, the blueprint will then be assigned on upload.

Files Section: Files section | Kirby CMS
Files field: Files | Kirby CMS

I don’t really understand what that means, sorry.

Do I have to name the Blueprint as the Subpage just store it once in the page folder for the page and once in the files folder for the files? Like that?
/site/blueprints/pages/subpage.yml (for general subpage)
/site/blueprints/files/subpage.yml (for all files of this subpage?)

Cause that’s what I did and nothing happens… If I upload an image there is just the default.yml “assigned” to it. I don’t get how I make Kirby load the /site/blueprints/files/subpage.yml