How to Create and Delete References Between Entities

How do I post and put related entities. I have a Product entity for example with a Supplier navigation property. I would like to have an endpoint that allows to change the supplier for an existing product. Using odata I was able to make a post endpoint for the Product, but if I tried to include the supplier it had to be a new supplier, an existing one would through an error regarding the same primary key already exists. I am trying to allow posting an existing supplier and only binding it, without trying to create it.
I found a tutorial on microsoft.com, where they showed how to use CreateRef and DeleteRef. I tried to implement the same thing, but the endpoint wasn't even created. I assume the tutorial was for an earlier version, I am using odata 8.0.0-rc. I tried cloning the repository and running the sample project. But the above methods seem to not really be implemented (they return a string), and the endpoint is not mapped anyhow.
So, I am looking for an example on how to implement the above behavior. Any help would be appreciated, and I am sorry if I missed something obvious.
Thanks, Michael.

Start with the sample project and the CreateRef/DeleteRef implementation described in the issue, then inspect how its endpoints are mapped in the OData 8.0.0-rc setup. Confirm whether existing related entities can be bound without creation, and document or demonstrate the supported behavior when the endpoint mapping is complete.