Hello, Andrew.
I'll show you how you can delete a customer in QuickBooks.
You can delete the customer by inactivating them from your Customers list. Here's a step-by-step process:
- Go to the Sales menu on the left panel.
- Click the Customers tab.
- Find the customer that you want to remove.
- Click the arrow icon beside the Create invoice link (under ACTION).
- Select Make inactive.

Take note that this won't entirely remove the customer from your list. This will just inactivate them so you won't be able to see their profile when creating transactions.
Do you need help creating invoices? Or perhaps do you need to customise your sales forms to better present your business? You can take a look at these articles for a guide:
You're welcome to ask again if you have more questions about your customers or their transactions in QuickBooks. Just reply and I'll jump right back here.