How/Where to add my Google Analytics account ID in my third party domains?

[KikiS]

I have just recently added a .nl & .it domains to my shopify account (as third party domains) for international selling/seo reasons.

Now I want to make sure the visitors from my .nl & .it accounts aren't seen as referrals but are measures as visitors from the same Google Analytics (GA)account.

I have read this discussion/post on the community, It does explain what to do but not how to do it in Shopify.

It's not clear to me where/how I can reach the code of my .nl & .it domains.

Can anybody help me out?

Thanx in advance

Kiki

p.s. I'm not a developer although I understand some basics