This is how I get first image from gallery.
<?php
$images = get_field('gallery_images');
if( $images ):
$image_1 = $images[0];
?>
<a href="<?php the_permalink(); ?>">
<img src="<?php echo $images[0]['sizes']['medium']; ?>" alt="<?php echo $image['alt']; ?>" />
</a>
<?php endif; ?>
Hope it helps 😉
