Google COnversion code

How do you add the HTML Google Code for Conversion Page to the Fast Contact form.
To the auto response page like a “thank you for filling the form”.

Or do I create a page with the code and link the page to the response. But which field do I use?

https://helpinghand.com.au/contact-us/

https://www.ads-software.com/extend/plugins/si-contact-form/