I'm working on my 2020 & 2021 taxes. I did a 401K withdrawal for the COVID relief & forgot to put my 2020 taxes. Can I put it on my 2021 taxes?

My 2020 and 2021 taxes have not been submitted yet. Should I redo my 2020 taxes and include the 1099R or can I put it on my 2021 taxes since the income can be spread out across 3 years?