The IRS requires that you file the 2018 tax return before requesting a tax installment plan.

Complete and file the 2018 tax return.  Since taxes are owed and you are going to request an installment plan, in the File section indicate that you will be paying the taxes owed with a check that would be mailed to the IRS.   You do not mail the check but complete the payment plan request once the IRS has Accepted your e-filed tax return.

You complete your tax return by finishing all 3 Steps in the File section. In Step 3, to e-file your tax return, you must click on the large Orange button labeled "Transmit my returns now".

After completing the File section and e-filing your tax return you will receive two emails from TurboTax. The first email when your tax return was transmitted and the second email when the tax return has either been accepted or rejected.