A capital loss has to be carried over from year to year until it's used up. You can't skip a year. If it wasn't on your 2018 tax return you can't put it on your 2019 tax return. You'll have to figure out why it's not on your 2018 return. If it's not there because it was used up in 2017, then there is no loss to put on your 2019 return. But if it's missing from your 2018 return because of a mistake, you will have to amend your 2018 tax return to include the capital loss carryover, in order to calculate the amount that you can carry over to 2019. You don't have to wait for the IRS to process your amended 2018 return before you file your 2019 return, but you need the information from the recalculated 2018 tax return in order to correctly calculate the capital loss carryover to 2019.
To enter the capital loss carryover in your 2019 tax return, type "capital loss carryover" (without the quotes) in the Search box, then click the link that says "Jump to capital loss carryover." When it asks whether you know your capital loss carryover amounts, select "No, I need help figuring out my capital loss carryover amounts". Then enter the information that it asks for from your amended 2018 tax return and TurboTax will calculate the amount to carry over to 2019.
