You’re confusing the 6-digit IRS-issued Identity Protection (IP) PIN with the 5-digit user-generated PIN you create when you sign the online return. Those are different PINs.
Find the “Other Tax Situations” tab in your version of Turbo Tax. In my version (Home and Business) it was on the Personal tab where I entered personal income. On the Other Tax Situations tab, you should see a place to enter an IRS-issued 6-digit pin.
