Deductions & credits

You can go through the section "W-4 and Estimated Taxes" to figure your customized 1040-ES quarterly tax payments for 2019.    There is also a place in that interview to enter what you have already paid for 2019 (if applicable), and it will let you include any expected income changes or any other changes you have for 2019.

• Log in, and as you mentioned above, if TurboTax thinks you are finished, you likely will no longer have the "Take me to my return" button.  If you do have that button, use it to get into your return.  If not, you'll need to open your return back up in the following manner:
• Go to the section "Your Tax Returns & Documents".  Click on that line or the word SHOW to expand, then choose 2018.
• Choose "Add a State."  (you don't really add one; that's just to get the return to open back up.)
  
• Once the return is open and past the blue-green screen, click in the left menu column on Federal.
  
• Then at the top choose subtab "Other Tax Situations"
• Scroll way down to the last category "Other Tax Forms"
• Find topic "Form W-4 and Estimated Taxes" and click Start or Update.
• If you need to adjust withholding, go through the W-4 interview.
  
• If you don't need the W-4 (withholding) interview, you can skip that part and go to the 2019 estimated taxes interview.
• You may get a screen that says "Review your Estimates for 2019?" and asks "Do you want to adjust/review your income or deductions".  Say YES (or Review Now), so you can get to the additional questions.
• You will go through a lot of screens asking about expected income and deductions.
• Finally, you will come to a screen that says "Enter Payments You Expect to Make."
• There are some boxes there that say "Enter estimated tax payments you've already made for 2019."  
• Next screen will ask "which method" to use to calculate your 2019 estimated payments.
• Next screen will ask if you want to print vouchers.