Change Upload Folder Permission to 755

add_action( 'init', 'cf7_mfu_change_folder_permission' );

function cf7_mfu_change_folder_permission() {
    if ( defined( 'wp_dndcf7_upload_folder' ) ) {
        $upload_dir    = wp_upload_dir();
        $upload_folder = $upload_dir['basedir'] .'/'. wp_dndcf7_upload_folder;
        if ( is_dir( $upload_folder ) ) {
            chmod( $upload_folder, 0755 );
        }
    }
}