2 Shopify Store/Accounts - how to make one a subdomain of the other?

[lkstar]

I have a live store (maziandzo.com) that has earned a good amount of SEO value. I am moving some of the merchandize from mazi + zo to a new shopify store, which is also a new account mazinewyork.myshopify.com. I have been advised that it would be advantageous to Mazi New York's SEO if it's set up as a subdomain of mazi + zo. 

Shopify's AI helper says this is possible (see below) but when I follow the directions to set up subdomains on godaddy, I cannot get the new store connected to shopify correctly.

2 questions:

1. am I working too hard on this? Will the SEO cred from mazi + zo help the new Mazi New York?

2. can anyone help me find an expert in this? I've tried two upwork consultants and neither could figure it out.