If the IRS has closed your 2020 tax year as being completed, then you probably need to file an amendment for 2020. IRS does allow you to e-file an amended return. You could amend your return, carry forward to 2021 the $15,000. Prepare but hold off filing your 2021 until you get close to the deadline. or you see that your 2020 amendment was processed. If necessary, you could even file an extension showing on the extension the amount of the $15,000 and pay any additional tax over the $15,000.
