function post_date_update(){
    $args = array(
        'post_type' => 'post',
        'posts_per_page' => -1,
    );
    $wpost = new WP_Query($args);
    if ( $wpost->have_posts() ) :
        while ( $wpost->have_posts() ) : $wpost->the_post();
        $update_params = array(
            'ID'           => get_the_ID(),
            'post_date'   => current_time('mysql'),
        );
        wp_update_post( $update_params );
    endwhile; wp_reset_postdata(); endif;
}
add_action( 'init', 'post_date_update' );