If you have never claimed any vehicle expenses on your tax returns in the past, then in they eyes of the IRS, 2019 is the first time you started using the vehicle for business purposes.
You only need to consider past years of use when it has been claimed on a tax return.
If you took mileage the year before that (2017) use that answer.
The reason TurboTax is asking this question is because if you took actual expenses then you need to use actual expenses for as long as you use that vehicle for business.
Here is a TurboTax Help Topic that covers this in more detail: Using Mileage and Actual Expenses
What if 2019 was my first time ever deducting miles but I started using the vehicle for the job in 2018? @KarenM90
If you have never claimed any vehicle expenses on your tax returns in the past, then in they eyes of the IRS, 2019 is the first time you started using the vehicle for business purposes.
You only need to consider past years of use when it has been claimed on a tax return.