How do I know if I applied 2020 refunds to my 2021 taxes

You will need to access your 2020 federal tax return Form 1040 and look at Line 36.  If Line 36 shows an amount then that is the amount you requested to apply to your 2021 tax return.

To access your prior year online tax returns sign onto the TurboTax website with the User ID you used to create the account - https://myturbotax.intuit.com/

Scroll down to the section Your tax returns & documents.  Click on the Year and Click on Download/print return (PDF)

If you used the desktop CD/Download editions installed on your computer, the only copy of your tax data file and any PDF's will be on the computer where the return was created.  TurboTax does not store online any returns completed using the desktop editions.

Or go to this IRS website for free federal tax return transcripts - https://www.irs.gov/individuals/get-transcript

For a fee of $43 you can get a complete federal tax return from the IRS by completing Form 4506 - http://www.irs.gov/pub/irs-pdf/f4506.pdf