Delete an Azure Active Directory tenant – Microsoft Entra

Select Azure Active Directory. On a tenant’s Overview page, select Manage tenants. Select the checkbox for the tenant that you want to delete, and then select Delete. If your organization doesn’t pass one or more checks, you’ll get a link to more information on how to pass. After you pass all checks, select Delete to complete the process.

https://learn.microsoft.com/en-us/azure/active-directory/enterprise-users/directory-delete-howto