The first item you will need is Active Directory Domain's GUID of your Azure tenancy associated with Office and Dynamics 365. To get this ID, you will need to log in to your Azure tenancy as an administrator. If you are using the old portal, you will have a list of the directories under ACTIVE DIRECTORY. Click on the name of the correct directory and the GUID will be in the URL.

If you are using the new Azure portal, click on the help menu at the top right, ? | Show diagnostics (as per the following screenshot), and you will be prompted with a JSON dialog. Locate the tenant object with the correct domain name. The GUID will be the ID of that JSON object in the array:

The JSON object will contain an array of tenants that look like the following:

"tenants": [ 
    { 
      "id": "00000000-0000-0000-0000-000000000000", 
      "domainName": "packt.onmicrosoft.com", 
      "displayName": "Packt", 
      "isSignedInTenant": true 
    } 
  ] 

Alternatively, you can also retrieve your tenant GUID using the following PowerShell script:

Login-AzureRmAccount 

Check this article for details at https://support.office.com/en-us/article/Find-your-Office-365-tenant-ID-6891b561-a52d-4ade-9f39-b492285e2c9b