Trying to modify keys to left and right arrow keys but doesn't work

I have this Json file and it does not apply to the left_arrow key. But it is mapped with something else. How can I find my keyboard key to find what is which 'key_code'?

{
      "title": "For Korean PC Keyboard",
      "rules": [
        {
            "description": "Change Kor/Eng key to command+space",
            "manipulators": [
            {
              "from": {
                "key_code": "lang1"
              },
              "to": [
                {
                  "key_code": "left_arrow",
                }
              ],
              "type": "basic"
            }
          ]
        },
        {
            "description": "Change Hanja key to option+return",
            "manipulators": [
            {
              "from": {
                "key_code": "lang2"
              },
              "to": [
                {
                  "key_code": "right_arrow",
                }
              ],
              "type": "basic"
            }
          ]
        }
      ]
    }