For more help reporting Adjusted Gross Income, see: How do I find last year’s AGI?
Regarding reporting additional income, yes, an amended return would be required. See: How do I amend my 2020 TurboTax Online return?
It is possible to file a second amended return following the same steps as listed in the article posted above.
The IRS will otherwise send a notice for the missing income. There may be penalties and interest charged for underreporting the income if the income was not corrected by May 17 or there was no extension filed. See: How do I file an extension?
Save a PDF of the original and the first amended return before beginning the second amended return.
To download the PDF, follow these steps:
- From the left menu, select Tax Home.
- Scroll down to Your tax returns & documents and Show.
- Select 2020 for each return listed.
- Navigate to the option to download the PDF of your return.
State amended taxes can be e-filed only in Georgia, Michigan, New York or Vermont. Otherwise, they must be paper filed. See: Do I need to amend my state if I amend my federal?