I have LT Capital Loss Carryover from 2016 Turbotax return. Somehow, it wasn't captured in my 2017 or 2018 Turbotax return, how to report carryover in 2019 TT return?

A capital loss carryover has to be carried over from year to year until it's used up. You can't just take the carryover from your 2016 tax return and enter it in 2019. Some of it would probably be used each year, even if you did not have any capital gains. You will have to amend your 2017 tax return to include the capital loss carryover from 2016. If it's not used up in 2017, you will have to amend your 2018 tax return as well. Then you will be able to enter the information from your amended 2018 tax return in TurboTax for 2019, so it can calculate the amount that is carried over to 2019, if any.

You don't have to wait for your past-year amended returns to be processed before you file your 2019 tax return, but you need the information from the recalculated 2018 tax return in order to correctly calculate the capital loss carryover to 2019.

For all years, when TurboTax asks if you know the carryover amounts, do not answer Yes. Select the option that says you need help figuring out the carryover amounts. You will then enter information from the preceding year's tax return so that TurboTax can calculate the correct carryover amount.