How to connect SUBdomain externally if ROOT is already connected to VZY?

Hi there,
I have succesfully connected my root domain tobias-haupt.de (my name) with VZY and everything works fine so far.
My question: I would like to blog regularly on GHOST and connect my blog on GHOST under the subdomain “blog.tobias-haupt.de
Is that possible and if so, how?
Thank you, kind regards!
Tobias