I would send back the notice with an amended 2021 Iowa return showing only the 2021 w-2. include a letter of explanation. something like. I'm submitting an amended return because I accidentally included a 2020 W-2 on the original 2021return. Don't know what your 2020 Iowa return would be like, but I would include the 2020 return and change the explanation accordingly. this would require either manual preparation or the purchase of TurboTax desktop software.
It's not clear if you've gotten a notice from the IRS about 2021? generally, you should not submit an amended Federal return until the original is fully processed. in some cases like this, the IRS may change your return automatically with no need to file an amended return. don't know about 2020.
here's a link to 2020 IRS instructions so you can determine if you must file. if you do or want to in order to get your refund, it must be mailed in.
https://www.irs.gov/pub/irs-prior/i1040gi--2020.pdf
