I lost all 2020 records and have downloaded a irs file for 2020 how can I get it to import to a reinstall 2020 turbotax

You cannot use the IRS transcript or the IRS copy of the 2020 return to transfer to the 2020 TurboTax program.

However, you can use the information in the transcript or copy to re-create the 2020 tax return.

I did this for 2021 and now have IRS documents, what do I input from them to create last years file?

If you are planning to amend, Form 1040-X will reflect the differences from your revised correct 2021 return, and your 2021 transcript.

There are other internet services that will let you redo your 2021 tax return, correctly, for no charge.

Or use TurboTax 2021, or other means.

@Mikros