I can see how challenging this has been, Gbaker. You can delete a customer by making them inactive, and this option is only available in the web version, not on the mobile app.
Once you're on a web browser, log in to your account and go to Customers and goals > select Customers > hit the dropdown arrow next to Send reminder > Make inactive, then Yes, make inactive to confirm.

If you need to inactivate multiple customers at once, tick the checkbox next to each customer you want to delete and use the Batch actions menu to proceed.

You can also navigate through this article for more info: Delete customers in QuickBooks.
If there is anything else I can do to help you, add a Reply below.