minutpa, I assume that you mean that you failed to take the distribution in 2019 rather than that you took the distribution in 2019 but just failed to report it. If you took it and failed to report it, amend your 2019 tax return to add this income as DanaB27 describes. Otherwise, all you need with respect to your 2019 tax return is to file 2019 Form 5329 as I describe below.
If you didn't receive a late distribution of the 2019 RMD in 2020, nothing about this goes on your 2020 tax return.
Assuming that you have not yet taken this missed 2019 RMD, you should take the RMD now, then file 2019 Form 5329 requesting waiver of the 50% excess contribution penalty. This distribution will then be reportable and taxable on your 2021 tax return along with the 2021 RMD from this account. See the last page of the instructions for 2019 Form 5329 for requesting the penalty waiver:
https://www.irs.gov/pub/irs-prior/i5329--2019.pdf
