Generally, the answer is to enter the information as it appears on the letter. However, if your numbers are definitely incorrect and are causing you to enter twice as much as you actually received, you will need to call the number on the letter and speak with the IRS to fix it. The number is 800-908-4184.
If you are sure it is incorrect, you should hold off on filing your tax return until you speak to them and get an updated corrected amount or a correct amount in the portal.
I have this problem, too! In TurboTax, I clicked on, "What if the amount from my letter doesn't match my records?" and then logged into my personal account on the IRS web site as suggested by the TurboTax On Demand Tax Guidance to check my "2021 Advance Child Tax Credit Payments Information." Here's what the IRS directed there:
"If There Are Differences With the Amounts From Your Mailed Letter 6419
Use the information shown on this page when filing your 2021 tax return to avoid any processing delays. The amount on this page is the most accurate information about the advance Child Tax Credit payments."
So, the IRS says ignore the Letter 6419 amounts and use the figures displayed for you on the IRS web site.
If the IRS updated the amount you received as Advanced Child Tax Credit Payments and that figure no longer matches Letter 6419, enter the updated amount and answer "Yes" to the question TurboTax ask regarding if it matches.
The question "Does this amount match?" is a TurboTax question to try to limit errors. It is NOT an IRS tax question and is not reported on Schedule 8812 or any other tax form.