Go to Maintenance option > eMail Lists > Mailing List - Mail Chimp > The required fields are API Key and List ID.
Find or Generate Your API Key:
- Click your profile name to expand the Account Panel, and choose Account.
- Click the Extras drop-down menu and choose API keys.
- Copy an existing API key or click the Create A Key button.
- Name your key descriptively, so you know what application uses that key.
To find LIST ID you need to go in mailchimp.com > Lists > Choose your list > Settings > List name and defaults.