This post describes how to link your Microsoft partner ID to an Azure tenant
Change by GUI
Log in azure with the credentials of the customer
Use this link:
https://portal.azure.com/#blade/Microsoft_Azure_Billing/managementpartnerblade
Fill in your partner ID
Click on Link a Partner ID
The portal is now linked to your subscription.
Change by Powershell
Install module AzureRM.ManagementPartner
Install-Module -Name AzureRM.ManagementPartner
Find the tenantID
Go to Azure Active Directory => Properties => Directory ID
Connect powershell to the tenant
Connect to Azure :
Connect-AzureRmAccount -TenantId XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX
Error message when no connection is linked
New-AzureRmManagementPartner -PartnerId 12345
Check the connection.
Delete an existing link to the partner ID
Remove-AzureRmManagementPartner -PartnerId 12345 -PassThru
Documentation
For more information you can check the site of Microsoft: