Reviews Tab always show on single product page.

     $args = array(

        'post_type'      => 'product',

        'posts_per_page' => -1

    );

    $loop = new WP_Query( $args );

    while ( $loop->have_posts() ) : $loop->the_post();

              global $product;

$product->set_reviews_allowed( 'yes' );

$product->save();

    endwhile;

    wp_reset_query();