There is no simulation program for 2019 taxes using the online product. Tax law for 2019 is expected to be nearly the same as for 2018. You can use TurboTax TaxCaster to simulate 2019 taxes based on 2018 tax law: https://turbotax.intuit.com/tax-tools/calculators/taxcaster/
Or you can open your 2018 tax return and type estimated taxes for next year in the search box and click on jump to estimated taxes for next year and use that part of the 2018 program to estimate 2019.
Make sure you don't make any changes to your actual 2018 tax return that you filed.