I assume that you received the payment in 2025. You will report the entire lump-sum payment on your 2025 tax return. You do not amend your 2024 tax return. There is a "lump-sum election" that might reduce the amount of the payment that is taxable. Essentially what the lump-sum election does is calculate how much of the payment for 2024 would have been taxable if you had reported it on your 2024 tax return, and then include that amount in the taxable Social Security on your 2025 tax return.
Your SSA-1099 for 2025 will show how much of the payment is for 2024. After you enter the SSA-1099 in TurboTax, it will ask if you received any lump-sum payments. If you answer Yes it will then ask for information about the lump-sum payment for 2024. It will also ask for information from your 2023 SSA-1099 (if you got one) and your 2023 tax return. After you enter all the information, TurboTax will calculate whether you benefit from using the lump-sum election. If so, it will make the appropriate entries on your Form 1040.
