Checkbox for Login/Register form

Hi,

By using the "login/register form" widget by the "essential addons" plugin for elementor I have created a login/register form. The only issue is that I would like to add a constant contact subscribe checkbox on the form but can't seem to make it happen. I've attempted to install the constant contact plugin and enable "Add a checkbox to the WordPress user registration page" but it only applies it to my current registration form that I've created using a third party plugin called "Ajax Login Register Modal". Is there a code or any suggestions to guide me to my request. Thank you very much for your time and help!

Wilard