When you are creating a new Customer in Dynamics 365 CRM, and if you want to associate its Parent Company then you can follow below steps,
1 – Log in to your https://home.dynamics.com page and click your company app.
2 – Then you would need to click Sales then Accounts, and Create a new account.
3 – Create Parent Company and define the Relationship as Customer. In this example Department of Education and Training is my test customer and a Parent Company. Click Save and Close now
4 – Now, create a new Child Company in a similar manner but define name of the Parent Company in the Customer page and associate with it, under Parent Account. Click Save and Close
5 – Define other details if you want to.
I have created an example using Department of Education and Training as Parent Company and Victorian School Building Authority as child Customer. These are my test customers.