Which year do I enter a "backdoor Roth" conversion? I contributed to a Roth last year, recharacterized to Traditional early this year, and then converted back to Roth.

I have been contributing to a Roth IRA for years but turned out to be ineligible (income too high) in 2019. To avoid the penalty, I recharacterized the entire 2019 amount to a Traditional IRA in March 2020. I then converted it all back to a Roth ("backdoor" style) shortly after. Do I need to enter this backdoor conversion in my 2019 taxes, or only next year? Not sure if I should select that I contributed to a Traditional IRA, since technically, I did not.