My new customer got 2nd Stimulus Payment on January 4th, 2021. His tax preparer didn't put this payment in his 2020 tax return, because he said it was in 2021 so will be used in next year return, and in the return of 2020, which he did in March, he said that he did not get it. As a result, my client received the second payment twice (as direct deposit on 01/04/2021 and as a Credit in his 2020 tax return). Should he submit an amended return for 2020? Or maybe he must show in the 2021 return that he got both the third and the second? Or any other option?

I would be grateful for any suggestions.

Thank you.