Hi Hollis,
Thank you for reaching out! Normally you would add JavaScript to your theme using the Custom CSS and JS Editor. The guide I linked you to is for our Crio Pro WordPress theme but most themes have a similar method to add CSS and JavaScript directly.
You could also use a Code Snippets plugin or add the Javascript directly to a theme file in your WordPress theme structure. It would likely depend on how your affiliate partner prefers the code to be added so it would be best to contact them and ask where it should be added. I’m sure they have some documentation on this.
I hope this helps!