Thanks for reaching out in the Intuit Community, angela9,

Let me get the help you need in setting up a Parent and Sub-customer in QuickBooks Online. 

To have the Parent customer's address shows up under Bill and your Sub-customer under Ship to, here's what you'll need to do:

1. Click Sales in the left navigation menu, then go to Customers tab.
2. Click the name of the sub-customer.
3. Click Edit button at the upper right hand.
4. In the Customer information window, click on Address tab.
5. Enter the Parent address in the Billing address section, then enter the sub-customer address in the Shipping address.
6. Click Save.

That's it! For additional reference, I've included some helpful articles that you can check: 

• What does the bill with parent feature let you do on invoices?
• How to add a customer or sub-customer

If there's anything else you need help with in setting up customer's in QuickBooks Online, please let me know. I'm always here to help. Have a great day!