How can I change the default domain in my Shopify back office?

hello can anyone help me with changin this domain that shopify generates for you jayzjewels-563f.myshopify.com-shopify1

context: i had a previous store before jayzjewels.com/uk which i have now rebranded to javanblake.com/uk i have changed the domain name and on my hosting provider which is showing correct but from tine to time when i am personally navigating through my shopify back offfice jayzjewels-563f.myshopify.com-shopify1 will still be the main domain. its also showing on most of my facebook ad and business manager accounts which is proving quiet difficult to change. but first and foremost i would like to get rid of my previous domain jayzjewels-563f.myshopify.com-shopify1

Hi, @JavanBlake !

The custom domain you purchased is what customers will see on your online store as long as it is set as your primary domain, but your admin is supposed to show your myshopify URL. This is the free URL that remains part of the admin regardless of the custom domains you connect.

Regarding your Facebook accounts, is the myshopify URL showing up on your ads, or only in the admin?