How to setup Heads with 2 SSD drives

I bought the Nitropad x230 and I want to use 2 drives, one SSD internal and one SSD external and remove what comes by default and install my own Linux distro on both after formating them.

Can someone explain how to do the signing of the boot files etc for each drive so both work with the nitrokey to get the green light?

I’ve tried reading the wiki and it’s not clear to me. Also there are no videos on Youtube. You should make tutorials or something.