How do I revise 2018 estimated tax? I had a one time capital gain on company stock setback when I retired.

To revise your current year estimated tax payments due in TurboTax Online:

Select: Federal>Other Tax Situations>Form W-4 and Estimated Taxes and press "Start" (or "Revisit").

1. Click on "No" to the question: "Do you want to change your W-4 withholdings for 2018?" 

2. Select "Prepare Now" to make any necessary adjustments to your 2018 income and deductions with estimated tax payments.

Your state estimated tax liability for the current year will automatically be transferred to your state return.