Button options Markdown field in Blocks fieldsets

Could someone plz tell me how to add the buttons settings for the Markdown field in a blocks fieldset? The underneath doesn’t work …

          blocks:
            type: blocks
            fieldsets:
              - heading
              - text
              - columns
              - markdown
                buttons:
                  - blockquote
                  - pagelink
                  headlines:
                    - h1
                    - h2
                    - h3
                    - h4
                    - h5
                    - h6

So, this was the wrong path, obviously. Added a markdown.yml file to blueprints > blocks and set those button options in that file.