You wrote: E-file

Yes, a 2018 return can be efiled with TurboTax.   Prior-year returns have to be printed, signed, dated, and mailed.

I need to E-file my 2018 taxes.  I accidentally selected to mail in return.  However I would like to E-file what steps do I need to take to do this?

How to change from Mail to Efile

https://ttlc.intuit.com/community/e-file/help/how-do-i-change-from-mail-to-e-file-in-turbotax-online...