I received money that paid taxes in Korea. how to report it to IRS

Yes, you are correct.

If you inherit cash, you do no need to include this inheritance on your federal or state income tax return. (The estate (in Korea) will pay taxes on this money that you inherit but you have no filing requirement for inheriting the money)

As long as the decedent who transfers the asset by bequest is neither a U.S. citizen nor a foreign national domiciled in the United States, no U.S. estate tax is imposed on the transfer. The United States does not impose inheritance taxes on the beneficiary's receipt of a bequest, therefore there is no U.S. tax resulting from the death transfer

However, if you receive a gift or inheritance from a foreign person (nonresident alien) or from a foreign estate and the total amount during the year exceeds $100,000, you are required to report the gift on Form 3520. (This form is not supported in TurboTax). Please refer to this IRS link for more information on Form 3520:

https://www.irs.gov/instructions/i3520/

Please note that you may need to file an FBAR if the money was held in a foreign bank account under your name or if you had signature authority over a foreign account.

If you have foreign bank accounts, you may be required to file a Report of Foreign Bank and Financial Accounts (FBAR) if are a US citizen or resident and:

1. you had a financial interest in or signature authority over at least one financial account located outside of the United States; and
2. the aggregate value of all foreign financial accounts exceeded $10,000 at any time during the calendar year reported.

To be directed to the US Treasury Government Website to prepare a Report of Foreign Bank and Financial Accounts, click FBAR (TurboTax does not support this form)