Setting up a subdomain to point to a new Squarespace website

Site URL: https://jenniferarzt.squarespace.com/

Hi all,

My domains are now part of Squarespace (they were on Google Domains). I have my main website elsewhere and I've just built my shop on Squarespace. I'd like to create a subdomain for the shop on Squarespace and don't know how to get it done. (shop.jennfierarzt.com)

I thought the flow would be here:

From Domains > Website > Add Rule 

But as I was trying to get things set up I wasn't sure if I was supposed to forward from shop.jenniferarzt.com to the squarespace url? Or if there's a completely different flow to get this set up.

Thanks,

Jen