1. Register IMEI codes ( https://www.kimchimobile.com/how-to-prepare-smartphone-korea/ )
2. Turn off Roaming / eSIM / Dual SIM / Cellular / Wifi
3. Insert SIM card (You should take off other SIM if you are using Dual SIM)
4. Turn on only cellular and reboot
This process is to let your device recognize the new SIM card. If you put 2 SIM at once or turn on dual SIM program, your new SIM will not work. Please turn off and take out everything before activating your new SIM.
If you do not follow these instructions, your device might be blocked by the carrier center, so please READ and FOLLOW!