Where to edit the WPMU Dev link in footer of Product Theme

I'm using the Product Theme.(Child)
In the bottom left, there's the WPMU Dev link to your page.
I'd like to place my affiliate code in there.
Do I update the footer.php in the main theme?
How can I set this up in the child theme?
My guess is that I have to edit the child.css, but not sure how.

Thank you.