Form 8606 is cumulative. You only need the form from your 2019 tax return to prepare your 2020 tax return. You should be saving copies of all of your tax returns as PDF files or printed paper copies for at least three years after you file and preferably for six years, regardless of whether you save the software programs.
if you don’t actually have a PDF or a paper copy of your 2019 tax return, you can request a transcript from the IRS that will show the information that was on the form.
https://www.irs.gov/individuals/get-transcript
