I've filed and paid the Turbotax upgrade. I still have to pay my taxes balance due. How do I find Pay Simply in the program?

If you owe taxes, you would have been aske how you wanted to pay them before you filed your return. If you didn't choose to pay via any of the methods that involve PaySimply then, you will not be able to get back to that page.

This CRA website lists all the ways you can pay your taxes owing: https://www.canada.ca/en/revenue-agency/services/payments-cra.html