I have the Apple card and Apple savings account in my non-US region Apple account. How can I transfer it to my U.S. region Apple account?

There is no such thing as a transfer of Apple Card Mastercard, Apple Savings account and wallet data. What you can do is cancel all subscriptions, spend all the funds in the Korean Apple ID Account and change it to a US region account.

Do this first;

>>What to do before you change your country or region

• Spend any balance remaining on your Apple ID. If you're not sure whether you have a balance, check your Apple Account balance.
• Cancel any subscriptions that block a country or region change, and wait until the end of the subscription period. 
• Wait for any memberships, pre-orders, movie rentals, or Season Passes to complete, and wait for any pending store credit refunds to process. You can cancel a pre-order.
• Make sure that you have a payment method for your new country or region. See what payment methods you can use.
• Redownload your apps, music, movies, TV shows, and books on any devices that you might use to play or read them in the future. Some types of content might not be available in your new country or region. Learn what types of content and services are available in your new country or region.
• After you update your Apple ID billing address and payment method, you can upgrade your iCloud+ plan using the pricing in your new country or region.<<

Change your Apple ID country or region - Apple Support

Then change your Apple ID region to US following the steps in the article above. Log into iTunes and App Store and you should be set.