I modified this code after quickly learning how Wordpress plugins actually work, how they're called etc.. was the first trick to modifying the code to add tags.
Add this code after line 570 in wp-content/plugins/wp-instagram-post/classes/class-woo-igp.php
$tags = get_the_tags($post_id);
foreach( $tags as $tag )
$the_tags=$the_tags. "#". $tag->name;
$message = $message . "$the_tags";