/**
 * Callback function for the 'webmention_refresh' filter.
 *
 * @param mixed $commentdata 
 * @param mixed $comment_ID 
 * @return mixed The filtered value.
 */
function my_webmention_refresh_callback( $commentdata, $comment_ID ) {
    // Your code here.
    return $commentdata;
}
add_filter( 'webmention_refresh', 'my_webmention_refresh_callback', 10, 2 );

apply_filters( 'webmention_refresh', $commentdata, $comment->comment_ID )