Incorporate terms of use with the salesforce plugin

I need to incorporate the terms of use check box (agree to) on my registration form. I have created a new salesforce lead form to replce the Formidable registation form but I can not find where/how to add the terms of use check box to the registration page.

“I have read and agree to the Terms & Conditions “

I am working in the production environment and do not want to change the pages completely until I am sure.