To connect MailChimp go to Profile>Settings>API Keys, if you don't have any keys you may need to generate one.
Once you've got the key you'll need to paste this into Exsalerate (Settings>Mailchimp Integration> MailChimp API Key)
See screenshots below:
Log in to MailChimp and click on your profile
Click Extras > API Keys
Scroll down and click create a key
Copy the API key & Paste into Exsalerate.
Once you've created your key open Exsalerate and go to the MailChimp integration page. Menu > Settings > MailChimp Integration
Paste the key as shown below.
And that's it, click here to read about using MailChimp and Exsalerate.