How to add drop-down so user can choose a group to subscribe to

First create the interest group in your Mailchimp.com account under Audience > Settings.

Then in your WordPress admin go to MC4WP > Mailchimp and click “Renew Mailchimp lists” to pull in the latest changes you made.

Now go to MC4WP > Form > Fields, and click the name of the interest group above the form builder to insert that into the form, it will show you some options on how to add it (eg checkboxes or drop down etc).

Hope that helps. If you have any questions, please let me know!