Hey Samuel,
Thank you for reaching out to us!
Assuming that you followed the instructions in this article to include featured images to month view, you can simply replace this code:
<?php if ( has_post_thumbnail() && 1 == $day['total_events'] ) : ?>
<div class="tribe-events-event-thumb"><?php echo get_the_post_thumbnail( $post->ID, array(90,90) );?></div>
<?php endif; ?>
With:
<?php if ( has_post_thumbnail() ) : ?>
<div class="tribe-events-event-thumb"><?php echo get_the_post_thumbnail( $post->ID, array(90,90) );?></div>
<?php endif; ?>
on ‘wp-content/themes/[name of theme]/tribe-events/month/single-event.php’ to achieve what you want.
I hope this helps! Let me know if you need anything else and I’ll be happy to assist!
Regards,
Patricia