Google Workspace Transfer from One Domain to another

I purchased Google Workspace Gmail accounts for my domain I purchased through Squarespace. I decided to deprecate that domain and use a new domain I created in Squarespace. Since I paid up front annually, I wanted to switch my gmail accounts from abc@olddomain.com to abc@newdomain.com 

How would I go about doing this?

If both domains are connected to the same Squarespace site, you can make the new domain the primary domain. The old domain will still go to your site but the new domain will always show in the browser bar. This allows the search engines to catch up, at some future point you can disconnect the old domain if you wish.

Any third-party site should be able to do the same. 

Setting the primary domain.