You can't skip years. A capital loss carryover has to be carried over from year to year until it's used up. In order to use the loss at all, you have to file a 2018 tax return reporting it, even if you have no other reason to file. If the loss isn't used up in 2018, you have to carry it over to 2019, then to 2020. If you filed a 2019 tax return you will have to amend it to include the capital loss carryover. Then you will be able to enter the information from your 2019 tax return in TurboTax for 2020, so it can calculate the amount that is carried over to 2020, if any.
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 don't have to wait for your 2018 and 2019 original or amended returns to be processed by the IRS before you file your 2020 tax return, but you need the information from the recalculated 2019 tax return in order to correctly calculate the capital loss carryover to 2020.
And by the way, being a dependent does not mean that you don't have to file a tax return.
