If you are looking to find the Mailchimp API Key, Please follow the steps below.

Step 1: – Visit https://mailchimp.com/ and click on the Login link.

Step 2:-  Once you are logged in, You will see your Name on the right side top as shown below.

Click on It. You will see a dropdown like below.

Click on the Account link.

Step 3: On the account Page, you will see a horizontal menu. Click on Extra as shown below.

Ste 4:  Great, you are on the API Key page. Here you will see all your existing key and the option to create new key.

 And below that the create button

If you want to use existing key, Please use from your listed one or create a new key.