My school wants a digitally signed copy of my 1040

Self-prepared tax returns are not digitally signed.  The prior year AGI is used on the current tax year return for your electronic signature and to verify your identity on an e-filed tax return.

If the schools wants a signed tax return, then print the tax return, sign with ink on page 2 of the Form 1040 and give it to the school.

To access your current or prior year online tax returns sign onto the TurboTax website with the userID you used to create the account - https://myturbotax.intuit.com/

Scroll down to the bottom of the screen and on the section Your tax returns & documents click on Show.  Click on the Year and Click on Download/print return (PDF)

Or -

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 2019 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.  Choose the option Include government and TurboTax worksheets