Carryover loss for what? A rental property maybe?
"I want to know how you arrived at it if I did not due my taxed through Turbo Tax for 2017."
We need to know what you're talking about first. The carryover could be for rental or some type of business you have. Maybe you sold a rental or a business at a loss? Your reference to "not through TurboTax for 2017" begs the confirmation for just what tax year you are referring to. Are you working on your 2018 tax return?
So it appears that this conversation involves a 2018 income tax return and by your reference to "2017" I assume that you are referring to a carry over that came from 2017 or before, not a carry over that will now be available in 2020? And when you prepared your 2018 income tax return you didn't transfer information from a 2017 income tax return prepared using TurboTax?
If that's the case then the most logical explanation for that is that you entered that number as part of your input. There is an interview titled "Capital Loss Carryover" that's in the "Investment Income" section under the "Wages & Income" tab.
Did you start a 2017 tax return in TurboTax Online, but you didn't file it? If so, when you started your 2018 tax return in the same TurboTax account the information from the incomplete 2017 return would have automatically transferred to your 2018 return, unless you took steps to prevent the transfer.