NervesKeys without ATECC608A - where do keys go?

I’d like to get my device connecting to my custom NervesHub using debug keys before I permanently provision my ATECC608A. I’ve created test keys signed by my root-ca-key.pem based on this instructions NervesKey — nerves_key v1.1.0

Where do I put the device key and device certificate in nerves so NervesKey can use it without the ATECC608A? I’m testing on a Raspberry Pi 4.