Have you been otherwise able to add the domain to your settings > domains menu in your Shopify admin and just need to get this updated with the domain registrar?
Are you setting up a store for the first time here, and would this be for a new or existing business?
Don | Social Care @ Shopify - Was my reply helpful? Click Like to let me know! - Was your question answered? Mark it as an Accepted Solution - To learn more visit the Shopify Help Center or the Shopify Blog