Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Hello
Do you mean you want to add your company's domain to Microsoft 365 and have emails coming out with as ******@yourcompany.com?
If so, you need to use this instruction to add your company's domain to Microsoft 365 https://learn.microsoft.com/en-us/microsoft-365/admin/setup/add-domain?view=o365-worldwide&tabs=domain-connect
Once added successful, in Admin Center, you can go to Users > Active Users > YOur user, change alias, add an alias, you will find your company domain in the dropdown as an option for you to create an email address with that domain, then make that alias primary.