This is the exact plugin you need – https://wordpress.org/plugins/gallery-custom-links/
No code customizations needed.
For fixed image link (http://www.example.com):
$args = array(
'post_type' => 'post',
'name' => 'partners'
);
$logo_img = new WP_Query( $args );
?>
<div class="container-fluid" id="">
<div class="row" style="margin-top:1em;margin-bottom:1em;">
<?php if( $logo_img->have_posts() ): while( $logo_img->have_posts() ): $logo_img->the_post();
$logo_gallery = get_post_gallery_images( $post->ID );
if( $logo_gallery ): ?>
<div class="col-sm-12 col-md-12 col-lg-12 text-center">
<?php foreach($logo_gallery as $logo ): ?>
<a href="http://www.example.com">
<img class="img-fluid" src="https://wordpress.stackexchange.com/questions/351521/<?php echo $logo; ?>" alt="" width="60" id="partner-logo" style="margin:0 .5em 0 .5em;"/>
</a>
<?php endforeach; ?>
</div>
<?php endif; ?>
<?php endwhile; ?>
<?php endif; wp_reset_postdata(); ?>
</div>
</div>