Hi there, @nashtrap.

You can use the Add Job option to add a sub customer. When creating a sub-customer, you need to create a parent customer first. Let me walk you through the steps on how to create a parent customer. Here's how:

Create a parent account

1. Go to the Customers menu, then select Customer Center.
2. Click the New Customer & Job tab, and choose New Customer.
3. Enter the name of the customer.
4. Fill out all the necessary fields.
5. Click the OK button.

Add a Job

1. In the Customer Center, look for the customer that you want to add a sub customer.
2. Select the customer's name, then hit right-click.
3. Choose the Add Job tab.
4. Enter the job name.
5. Fill out all the information needed.
6. Hit OK.

Meanwhile, you can read this article in case you'll need help customizing customers report: Customize customer, job, and sales reports in QuickBooks Desktop.

If you have additional questions, please don't hesitate to leave a message in the comment section. I'll be happier to help. Take care and have a good one.