You can select to e-file your 2016 return in Step 3 of the File section of TurboTax. Keep in mind, that some returns simply can't be e-filed due to IRS regulations.
Sign in to TurboTax and continue your tax return by clicking the orange Take me to my return button. - If you originally selected to File by Mail, click Add a State to get back into your return and change your filing method
Click the File tab
Click Start next to Step 3
Choose I want to e-file and complete the File section
Click Transmit my Return to complete the e-file process
You have clicked a link to a site outside of the TurboTax Community. By clicking "Continue", you will leave the Community and be taken to that site instead.