As long as you haven't already mailed your 2018 paper return, you can switch to the e-filing method (through October 15, 2019)

However, some states now require e-filing, which means the federal and state must be e-filed together.

If you already mailed your return, don't e-file. This can cause problems with the government, including refund delays.

•  In TurboTax Online, sign into your account.Select File in the left menu.

• On the Just one more step screen, follow steps 1 and 2 if you haven't already
  
• Select the Start button to the right of Step 3.

• On the Let's get ready to e-file screen, select I want to e-file.
• Follow the instructions to e-file your return.