How do I change response text?

I’d like to change this text:

“Please sign up for at least one list.”

Do I need the form designer plug in?

Which plug in?

I see that there is a Constant Contact plug in for Gravity Forms. I believe that there is also a stand alone for WP. Which to use?

thanks

https://www.ads-software.com/extend/plugins/constant-contact-api/