Field to select customer contact in a form dropdown

Otherwise, when we create a form template, we would like to be able to select a customer contact in a dropdown.
So we can choose when to send to signature, then ko all customer contacts from tripletex came up.
This could be a field in the form as well?
Now it's manual with the text field.
But if you could select from a dropdown list, the customer's contact person and phone could appear in the report3)