I would not bother with a field for the Instagram URL. I would just have a “intagram user name” field and then if it’s filled in then output the url in code, something like this:
if (get_field('intagram_user_name')) {
?><a href="https://instagram.com/<?php
the_field('intagram_user_name'); ?>" target="_blank>Instagram</a><?php
}
Storing the actual URL to instagram for every user seems like a waste of DB space.