Many to many and Cred form

Hello,

I've looked at your user guide concerning many to many and find this option very interesting. The issue I have currently is to integrate this into a Cred form.

Let's take the example with rented cars : I have Cars People and then Agreements in order to make the link between car and people.
What I would like is to create a Cred form in order to create an Agreement in the frontend. For this, I need to select the car and the people and define some other info (start / end date, price …).

I'm not sure to understand how I can do this within Cred. When I create a Cred form dedicated for Agreement, I'm not able to make selection of the car nor the people, but perhaps I missed something?

Let me know
Regards
Pat