From your original question it sounds like your tax return is somewhat complex. The better course of action would be to open your original tax return in 2023 TurboTax, then use "Save As" to save a copy of it with a different name. (Add "amended" or "updated" to the name, for example.) Make the changes in the new copy of the 2023 return. Then start your 2024 tax return and, instead of transferring from the original 2023 tax return, transfer from the updated version. This will be safer than trying to make the changes in 2024 TurboTax, and less likely to cause errors.
If you use the 2023 software to make the changes, as I recommend, you cannot change AGI directly. You have to change the income items or adjustments that feed into AGI.
