If you are self-employed, you are required to file your business income (Schedule C) using your own accurate records of income and expenses, even if you don't get a 1099-NEC from all your clients. Assuming that to be the case, then you already reported all your income, and adding the new 1099-NEC won't change your taxes owed or refund due. You don't need to file an amended return. If the IRS sends a letter asking why you did not report the 1099-NEC, you can respond with a letter and a copy of your business records (like a PNL or other records) showing that even though you did not list the specific 1099 because it was late, you did fully and properly report the income.
If, on the other hand, you did not disclose this income originally, you will need to wait until your return is fully processed before you can file an amended return to add this extra income. The amending process won't be open until March.
