Is that the only estimated tax payment you had for 2018?   That 4th quarter data field is on the same page with the other 3 quarters, if applicable.

I can tell you how to quickly get to the estimated tax section to enter the payments.   You can enter the amount and the date the 4th quarter payment was made there.

I'm just curious if you had other payments why you are not seeing the 4th quarter field there.  But maybe this is the only one you had.

I went ahead and left you the steps and some screen images below.

Here's a shortcut to navigate to the estimated taxes section in the Online product to report the payments you made so you get credit for them.  There is a data field there for the 4th quarter payment. 

• Log in and open your return ("Take me to my return".)
  
• When the return is open, click at the top right corner on the Search tab.
• Enter quarterly without quotes and click on the magnifying glass icon.
  
• Choose Jump to quarterly.
• You will come to a screen "Estimates and Other Income Taxes Paid".
• The first topic is "Estimated Tax Payments."
  
• Choose the category(s) for the type of tax payments.

• Federal Taxes tab
• Then choose top tab Deductions & Credits.
• At the Tax Breaks screen choose to display All Tax Breaks.
• Scroll down to topic Estimates and Other Taxes Paid.
• Expand that section then choose  subtopic Estimated Tax Payments.
  
  

NOTE:  If you entered state estimated tax payments, then step through the State interview to be sure they transfer over to the state side.  Before filing, review your Federal and State return to be sure all payments are showing up.

These screen images are for the shortcut method: