If you already filed your tax return but left out a tax document then AFTER the return has been fully processed, you will have to amend the return to include that 1099G. But....what is the 1099G for? Is it for unemployment, or is it for something else like a state or local tax refund? If you did not itemize deductions on your 2022 return, you do not have to include the 1099G if it is for a state or local refund. If it is for unemployment you do have to amend and include it.