Hello,
1/ To answer your question, it’s best to refer to the plugin documentation or contact their support team directly. Here is the link to their support form: https://wordpress.org/support/plugin/mailchimp-for-wp/
2/ You mentioned that we solved a similar issue before, but there might be a misunderstanding, as such matters are not handled by theme authors. Could you please provide a link to the conversation where we resolved this issue? Here is an example of a different type of question: https://www.8theme.com/topic/mailchimp-for-wordpress-error-there-is-no-form-with-id-163-perhaps-it-was-deleted/#post-454982
Warm Regards,
The 8Theme Team