Contact Form – GD Ninja Form widget – configuration

I am trying to set up the Contact Form with the GD Ninja Forms widget. I have Ninja Forms set up and the GD Ninja Forms widget on the GD Page Details sidebar.

With reference to https://wpgeodirectory.com/docs-v2/design/gd-ninja-forms/

It says:

Visit the Custom Post Type settings -> Custom Fields
Make sure that the “Contact Email” field has been added to the Custom Post Type
Verify that the email field has the key ’email’

I am not clear as to where the Custom Post Type settings -> Custom Fields section is. The nearest I can find is Places –> Settings –> Custom Fields [Tab].

I have attached a screen shot as I can not figure out how to populate the ‘Custom Fields’ section which is displayed as ‘There are no custom fields here yet.’

Thanks.