Question: how to change my app store to korean?
Answer: Go to Settings.
In Settings, click iTunes & App Store.
Click on your Apple ID.
A pop-up will appear, click on the first option, View Apple ID.
Click Country/Region.
From the list, find and select 대한민국 (South Korea).
Click Next.
You will be redirected to the Terms and Conditions page, after reading, click on Agree.