How to create a yml file for files?

Hi - I have a section with files and I want to have a unique yml file for this specific files field.
this is tha page yml:

fields:
  photos:
    label: Book photos
    type: files
    uploads: book-img

and this is the yml for ‘book-img’ that is located inside blueprints/files/book-img.yml

title: book-img
fields:
  caption:
    label: Caption
    type: text

When I click on a file I get the message:

This file has no blueprint yet. You can define the setup in /site/blueprints/files/default.yml

but I don’t want to edit the default because I don’t want it to apply on all files.

I also tried the ‘accept’ property wwith no luck:

fields:
  photos:
    label: Book photos
    type: files
    accept:
      - book-img

thanks!

The first variant is correct, see

The template is assigned on upload, so won’t apply to already uploaded files

Aha it works for new files!
Thank you so much!