1. Go to the Form you'd like to add
Find the form in your library, and then click on it as though you were going to edit the form.
2. Click Share
Within the form, click the Share button in the top right corner, next to Preview!
3. Click on Share Form Link With Clients
Click on the little chain links to the right of the link!
4. Go to the Trip you'd like to add the form to
5. Paste the Link
You can paste the link or make it a hyperlink anywhere you'd like in the itinerary!
The Trip Description is a great place for it, as it's one of the first things a traveler will see when they open the Itinerary!