If you have already filed, you won't see the Take me to my return button any longer. To get back into the return, use the steps below. 

• Log into your account and click Tax Home to the left
• Scroll down and click Show More next to Your tax returns & documents
• Then click Add a state (not adding one, just a way to get back in return)
• Then click Federal to the left 
• And click Other Tax Situations at the top 
• Scroll down and click Start/Revisit next to Form W-4 and Estimated Taxes under the Other Tax Forms section

Or once you are inside the return again, follow steps here How do I print estimated tax vouchers for my 2018 taxes? and ignore number 1 there.