If you haven't filed then please follow these instructions to enter your quarterly estimated payments:

1. Login to your TurboTax Account 
2. Click "Take Me To My Return"
3. Click on the Search box on the top and type “estimated payments”.   
4. Click on “Go to estimated payments”
5. Click "Start" next to the estimated tax payments you want to enter

If your return has been already accepted by the IRS, you will have to file an amended return (1040X) to make changes. But you might want to wait until your refund or payment is processed. The IRS will only accept amended returns via mail.

Please see the following information on how to amend your return:

https://ttlc.intuit.com/replies/7276596