Add a file to the product

mutation {
  productAddAttributeValueTranslationsFile(input: {
    sku:"SKU77"
    attributeCode:"file_test"
    translations:{
      language:"pl_PL"
      value:"bike-1.jpg"
    }
  })
  {__typename}
}

Product, attribute, and file must already exist

value - path to the file

The MultimediaPath scalar type represents a textual combination of MultimediaFolderName, and MultimediaName joined with '/' Multimedia identifier pointing to its exact location.

The path to the file can be found with this query.