Assign a Directory for ACF Uploads

function field_name_upload_prefilter($errors) {
  //Add a WP filter that alters the upload path
  add_filter('upload_dir', 'field_name_upload_dir');
  return $errors;
}

function field_name_upload_dir($uploads) {
  //Change the path
  $uploads['path'] = $uploads['basedir'].'/tsf-xxx';
  $uploads['url'] = $uploads['baseurl'].'/tsf-xxx';
  $uploads['subdir'] = '';
  return $uploads;
}
add_filter('acf/upload_prefilter/name=tsf_file_upload', 'field_name_upload_prefilter');

tsf_file_upload = The ACF name

/tsf-xxx = Name of the directory in the uploads folder