How to create index on JSON field on nested key in PostgreSQL

Below is my JSON field data. Now I want to give index to key2_level_4, key1_level_3. How can I achieve this in PostgreSQL database.

[
  {
    "key_level_1": [
      {
        "key_level_2": "sample string data",
        "key2_level_2": "sample text",
        "key3_level_2": [
          {
            "key1_level_3": "label 1",
            "key2_level_3": "BHSBFKF",
            "key3_level_3": {
              "key1_level_4": 123,
              "key2_level_4": [
                "ARR_VAL_1",
                "ARR_VAL_2",
                "ARR_VAL_3"
              ]
            }
          },
          {
            "key1_level_3": "label 2",
            "key2_level_3": "JAHGFS KJH",
            "key3_level_3": {
              "key1_level_4": 123,
              "key2_level_4": [
                "ARR_VAL_1",
                "ARR_VAL_2",
                "ARR_VAL_3"
              ]
            }
          }
        ]
      }
    ],
    "key_level_1": "my value",
    "key_level_1": "my text"
  }
]

and after giving the index to that key, I want a select query that will filter the data based on it.