Connect a subdomain to Shopify

Hello,
I've been trying to add a subdomain through my dashboard in order to connect it to a Shopify store but unfortunately, I haven't been able to do that.

The problem is that, in order to connect the subdomain to Shopify it's necessary to configure both @ and CNAME, but when I add a new record for the subdomain I get an error saying that I can't add more than one record for subdomain.

What I'd like to do, basically, is to connect a Shopify store with a domain like this: shop.my-domain-name.com

Can you help me configuring it?

Many thanks