Specifically Link To the “Leave a review” part of product page? [closed]

You would probably need to do this with jQuery by detecting the hash value and activating the class based on that. Something like this might work:

add_action('wp_footer', 'custom_review_form_activate');
function custom_review_form_activate() {
    echo "<script>if (window.location.hash == 'review_form') {
        jQuery('.reviews_tab').addClass('active');
    }</script>";
}

(Of course if your theme or customizations already have some jquery you can add it there instead of in the footer like this.)