Hi Bobin,
If you’ve been using Office 365 for a while, you might have two public websites with the service (one created under the pre-upgrade version and another one created or to be created under the after the service upgrade version). You can keep and use both sites and share them publicly. But you can associate your custom domain with only one of these sites at a time.
If two public websites appear in Service settings > Manage public website in Office 365, you can decide which website—but only one website—to use with a custom domain. Click Change address next to the website that you want to use with your domain. In the drop-down list, select the domain name that you want to associate with the site, and then click Save.
To help you decide and learn more information regarding this matter, please read this article:
Work with your two Office 365 public websites
Thank you,
Paul Banez