In March of 2020, I put 6k in a roth ira (as my 2019 contribution) and 6k in an ira (as my 2020 contribution). Where do I enter the 2019 contribution?

[DoninGA]

You enter the 2019 contribution on your 2019 tax return.

See this TurboTax support FAQ for amending a 2019 tax return - https://ttlc.intuit.com/community/tax-topics/help/how-do-i-amend-a-2019-return-in-turbotax/01/123845...

[VolvoGirl]

But a ROTH is not deductible so it shouldn't change your 2019 return and you won't need to amend.  But you should fill it out to see if you were qualified to make a 2019 contribution.

[Critter-3]

Agreed ... you should amend to (1) see if you were qualified to make the contribution and (2) to see if you get any saver's credit form 8880.