Grab the adserver code by logining into the admin side, Pages, (Main Home) should look similar to this:
Find the expo banner in one of the Advertisement blocks - if you hover over the block you'll get a menu appear on the right hand side with 'edit, duplicate, delete' - hit edit and it'll show you the adserver code:
Onto the Adserver Plesk:
Find the domain we need to add it onto, then go into file manager and head here:

Edit this file:
related-posts.php
Copy and paste adserver code above header text as shown below