If you transferred last year's TurboTax return over, you don't have to do a thing—we've already entered it for you.
Otherwise, just open your TurboTax return, search for capital loss carryover, and then select the Jump to link in the search results.
We'll take you to the screen where you can enter that info from your prior year return.
Unfortunately, if the capital loss is not on the prior year's return, you will have to amend your returns so that the loss will show up on your 2018 income tax return. You cannot skip a year.