How to remove the message "Use PUT to insert or update list members"

I'm using JetPopup along with Mailchimp in a WP Theme. But while using the existing email, it showing

xxx.yyyy@gmail.com is already a list member. Use PUT to insert or update list members.

I want to remove this text "Use PUT to insert or update list members". But could not found on which file should I use. Please advice

Regards