How to declare 2018 Excess Contributions Discovered in 2020?

In 2020 I discovered that in 2018 I made excess contributions to my traditional IRA. Do I declare this mistake (and pay the penalty) when filing my 2019 or 2020 taxes?

 

Since I will be receiving the 1099-R for the removal of the excess distributions for my 2020 taxes I know that I will need to file Form 5329 with my 2020 taxes. Do I need to amend my 2018 taxes to include Form 5329 and should I file a form 5329 with my 2019 taxes?