Hi Alvin,
To add new fields to Easy Forms, you need to login to mailchimp (mailchimp.com) and define merge fields for your list. Once you add these fields in MailChimp, you will see the changes reflected in Easy Forms in WordPress.
Here is a guide from MailChimp about fields: https://kb.mailchimp.com/lists/managing-subscribers/manage-list-and-signup-form-fields
Also, we cache your MailChimp.com data in WordPress, so if you’re actively making changes in MailChimp and want to see the changes right away in WordPress, you’ll need to clear your API cache. It’s really simple. Here are the instructions: https://yikesplugins.com/support/knowledge-base/api-cache-settings/
I hope that helps – let me know if you have more questions,
Kevin.