Remember when Wix had an App in the App Market that allowed you to use Mailchimp on your site, and then they took it away? Yeah me too it was a sad day!
Welllll now they have a direct integration with Mailchimp, so wipe your tears away!
I made a short little tutorial video on this, I also provided a step by step process with screenshots below :)
Step By Step Instructions
1. Login to your Wix account and navigate to your Dashboard
2. On the left hand side click on Marketing Tools
3. On the left hand side click on Marketing Integrations
4. Scroll down just a little bit and click on the "Go for It" button on the Mailchimp Integration