First, you need to copy your tracking code for your specific campaign (here's how)
You have to ways to do so, depending on whether or not you want to add your form or pop-up onto all pages or one specific page.
In Project settings > Custom code, enter
your code in the Head code section, and Save changes.
Insert code before the closing head tag of your Webflow project
From inside the Designer, open Page settings, enter your code in the Head code section, and Save the settings. See which tags go in the <head> tag</head>.