Gaining access to the Azure AD / Entra ID B2C tenants before gracefully decommissioning it.

I am trying to gain access to many of the unused or neglected Azure AD B2C tenants that were created in my Azure platform https://portal.azure.com/#browse/Microsoft.AzureActiveDirectory%2Fb2cDirectories before decommissioning them properly using this article: https://learn.microsoft.com/en-us/azure/active-directory-b2c/tutorial-delete-tenant

Error shown:

The selected user account does not exist in tenant 'Product 1 B2C 001' and cannot access the application 'b3abd789-2a67-4ed3-bc18-9eaaa370be67' in that tenant. The account needs to be added as an external user in the tenant first. Please use a different account

Despite being the Global Administrator of my company's main Entra ID tenant, I am still unable to log in to these B2C tenants. My concern is that if I just click on delete the objects, the actual data in the B2C tenants are not deleted, which can be abused or concerning.

Any help would be greatly appreciated.