Authenticating
To connect the CRM to your Mailchimp account do the following.
Click your initials or profile picture and then click "Settings"
Find and click the "Integrations" tab on the left hand side
Find Mailchimp and click "Connect your account"
This will take you to the Mailchimp authorization page where you will enter in your Mailchimp username and password.
Once you confirm you will be redirected back to the CRM and your Mailchimp should say "Connected"
You are all set.