Mailchimp integration - prompt on order

-- url of the page with the problem -- : www.p3proswing.com
-- HikaShop version -- : 2.6.3
-- Joomla version -- : 3.6.4
-- PHP version -- : 5.6

We already have a newsletter module (Joomla->Mailchimp integration) on our page, but we'd like to prompt the user upon order to subscribe to our newsletter upon completion of their order.

Any ideas on how to accomplish this? Does Hikashop has this already integrated and I'm missing it? I want this to be optional and not something that automatically subscribes everyone upon order.