How can I add javascript to an external form embedded on a Wix page?

We have embedded an Eloqua form on our Wix webpage. To do so, we added an iFrame to the page and pasted in the HTML of the Eloqua form. However, the form is not capturing UTM parameters properly, so we need to add javascript to the form to enable us to do so. I have javascript but need to figure out where to add it. How/where can I add the javascript to the form?

Any insights would be appreciated!! Thank you.