How do I fix Duplicate, Google chose different canonical than user

[CameronO]

Hello, recently I had to change the domain of my store. Meaning that google had already indexed my product with the old domain, now I am unable to get the new domain indexed. Why is this? Furthermore, when I put in the old domain the shopify store is currently unavailable appears. Does this mean the domain is still linked to my store? I would really appreciate any help as my store doesn't appear in google searches as a result