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To send a text message from South Korea to China, the process is similar to sending a text message within the same country. The only difference might be the international dialing code or the network providers settings.
In English, it could be described as follows:
1、Open your phone’s messaging app.
2、Compose your message.
3、Input the recipient’s phone number, including the international country code for China, which is "+86". For example, if the recipient’s number is 1234567890 in China, you should input "+861234567890".
4、Send the message.
Please note that you may need to confirm with your network provider or messaging app for any specific settings or charges for sending international SMS.