How do I put `tax_query` in this WP_query?

Question

I can’t comment yet, but I would suggest first to modify your loop

<?php
// The Query
$query = new WP_Query( $args );

// The Loop
<?php if ( $query->have_posts() ) : ?>
    <?php while( $query->have_posts() ) : $query->the_post(); ?>
        <li><?php the_title(); ?> - <?php get_post_meta( get_the_ID() , '_event_start_date', true ); ?></li>
    <?php endwhile; ?>
<?php else : ?>
    <pre><?php print_r( $query ); ?></pre>
    <pre><?php print_r( $args ); ?></pre>
<?php endif; ?>

That way we can see the return from WP_Query. It could be it didn’t find any articles, could be an error, I won’t know.