add_filter( 'aioseo_llms_post_description', 'aioseo_filter_llms_post_description', 10, 2 );

function aioseo_filter_llms_post_description( $description, $post = null ) {

    if ( is_a( $post, 'WP_Post' ) && 14 === $post->ID ) {

        $description = 'This is a featured post. ' . $description;

    }

    return $description;

}