I filed and chose to print because I didn't have my 2018 tax refund but now I do and want to file electronically

[DoninGA]

You need the 2018 AGI (Adjusted Gross Income) amount to e-file a 2019 tax return, not your 2018 federal tax refund.

The 2018 AGI is on the 2018 Federal tax return you filed Form 1040 Line 7

See this TurboTax support FAQ for changing from mail to e-file - https://ttlc.intuit.com/community/e-file/help/how-do-i-change-from-mail-to-e-file-in-turbotax-online...

[VolvoGirl]

But if you already printed and mailed it do not efile it.  Only file 1 time.  

[Opus 17]

If you mailed your 2019 return, you can't file again. 

If you told Turbotax you wanted to file by mail, but never actually mailed your return, you need to contact customer support to reset the program so you can e-file.