I can provide you the step-by-step process in adding the percentage amount to show them on your invoices. Let me walk you through the process.
You might find this article interesting: Edit sales tax rate in QuickBooks Online. This will provide you details on what are the things to remember when editing a tax rate in QuickBooks.
Kindly update me on how things go by adding another comment below. I want to make sure you're all set, and I'm here if you need further guidance. Have a great day! All the best.