How to map a hidden field to a master-detail field?

I’m trying to add a survey to a custom object that is a child to parent object ‘contacts’. I’m passing the contact id as a hidden field and want to populate it back into the master-detail field in order to connect my custom object to the Contacts object. However, the master-detail is not appearing in the typeform form mapping in salesforce. Is there a workaround that will get me the same result?