When filling out the T4 section, the UI is missing a box for 17A. I can't fill out the amount for 17A that I can see. How do I enter 17A?

Which T-slips are you referring to? If you are using TurboTax Download and it is a T4A(P) double-click on box 20 and you will see the pop-up for the other boxes.

Thank you for choosing TurboTax.