Figuring out what taxable amount you previously used. Instr say: "Generally, the taxable amount would be on line 16b of your 2019 1040- there is no line 16b on my 1040?

The taxable amount of any pension/annuity received is shown on the 2019 Form 1040 Line 4d

This line number changed with the many changes made for the 2018 tax year but corresponding instruction in TurboTax was never updated to reflect that.  As DoninGA said, this instruction should say 2019 Form 1040 line 4d rather than line 16b.