function update_my_metadata(){
    $args = array(
        'post_type' => 'post', // Only get the posts
        'post_status' => 'publish', // Only the posts that are published
        'posts_per_page'   => -1 // Get every post
    );
    $posts = get_posts($args);
    foreach ( $posts as $post ) {
        // Run a loop and update every meta data
        update_post_meta( $post->ID, 'post_views_count', '0' );
    }
}
// Hook into init action and run our function
add_action('init','update_my_metadata');