I contributed $2,520.19 in 2019 to a backdoor Roth but was unaware that it was something that needed to be on the 2019 return. What steps do I need to take to amend?

You need to enter the non-deductible contribution in the year that the contribution was for in the IRA contribution interview.

 

You enter the 1099-R in the year converted.

 

See this TurboTax FAQ:
https://ttlc.intuit.com/questions/4350747-how-do-i-enter-a-backdoor-roth-ira-conversion

 

2019 and earlier can only be amended with TurboTax using the CD/download version installed on a PC or Mac computer.

 It is suggested that it be mailed certified with return receipt (or other tracking service) to verify that the IRS or state receives it.

See this TurboTax FAQ for detailed amend instructions:
https://ttlc.intuit.com/questions/1894381-how-to-amend-change-or-correct-a-return-you-already-filed

-- Amended returns can only be mailed - allow 8-12 weeks - can take up to 16 weeks (4 months) for processing.

You can check the status of the amended return here, but allow 3 weeks after mailing.

https://www.irs.gov/filing/wheres-my-amended-return

Thank you. So the online version of TT I am using now has a section for amending last year's return, so I am attempting to do that now.  I tell it that I have a form that I need to add to the return, and then that it is a 1099-R.  It then asks if I have retirement "income" for 2019, which is the only way to tell it that I need to enter the 1099R.  However, once I fill this out, I now have additional federal tax due.  This was after tax money I put into the IRA (and subsequent backdoor Roth), so why would doing this amendment result in an additional tax liability? 

Actually I see what I may have done..  I never entered the exact same amount from Box 1, gross distribution, for the amount I also CONRTIBUTED to the regular IRA for the year to take the deduction. So I am amending that as well. That zeroed it out.