function wpdocs_add_subscribers_to_dropdown( $query_args, $r ) {
$query_args[‘role’] = array(‘contributor’);
// Unset the ‘who’ as this defaults to the ‘author’ role
unset( $query_args[‘who’] );
return $query_args;
}
add_filter( ‘wp_dropdown_users_args’, ‘wpdocs_add_subscribers_to_dropdown’, 10, 2 );