Hello Hugh,
After you added your domain to Office 365, you can change the public-facing website address to your custom domain name, just as mchv2.0 mentioned above:
1.Log into Office 365 Portal, on the Admin page, in the left pane, click Domains under Management.
2.Click Change address, and then step through the wizard.
3.Choose the custom domain name from the drop down list.
For your reference:
Use a custom domain name for your SharePoint Online public-facing website address
Regards,
Cherry Wang
After you added your domain to Office 365, you can change the public-facing website address to your custom domain name, just as mchv2.0 mentioned above:
1.Log into Office 365 Portal, on the Admin page, in the left pane, click Domains under Management.
2.Click Change address, and then step through the wizard.
3.Choose the custom domain name from the drop down list.
For your reference:
Use a custom domain name for your SharePoint Online public-facing website address
Regards,
Cherry Wang