After you e-file the tax return and it has been accepted by the IRS, you do not print and mail the same tax return to the IRS.  There may be instances where you have to mail a certain form to the IRS but that would have been indicated in the Filing Instructions for your tax return.

Look at the Filing Instructions -

When you sign onto your online account and land on the Tax Home web page, scroll down and click on Add a state. 

This will take you back to the 2018 online tax return.

Click on Tax Tools on the left side of the online program screen.  Then click on Print Center.  Then click on Print, save or preview this year's return.