Begin by making your way to your Hero settings using the sidebar on the homepage, as seen below:
On the settings page, scroll down to the 'Product settings' cluster and click on 'Self serve products'. This will display a list of all of your current self serve products.
Next, find the self serve product that you wish to add a form to, and click the three dots on the right of the product. Then click 'edit'.
From here, scroll down to the 'Booking forms' section of the page and in the search bar, begin typing the name of the form that you wish to associate with the product:
Select the correct form and then click 'Save' in the top right corner.