JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE html>
<html>
<body>
<pre id="p1">Hello World!</pre>
</body>
</html>

JavaScript

const resp = {
  CBSServiceResponseDtls: {
    Response: {
      ResultStatus: {
        ResultCode: 0,
        ResultMessage: "SUCCESS",
      },
      Data: {
        EVENT: {
          API_OUTPUT: {
            SUCCESS_FLAG: 0,
            REQUEST_STATUS: 0,
            ABILLITY_REF_NUM: 32038,
            RESPONSE_ERROR_CODE: "",
            SUCCESS_MESG_LANG_1: "Request has been Processed Successfully",
            SUCCESS_MESG_LANG_2: "Request has been Processed Successfully",
            TRANSACTION_LOG_REFERNCE: 2.0200507064507202e27,
          },
          LOGIN_DETAILS: {
            LOGIN_DTLS: [
              {
                LOGIN_NAME: "soban",
                LOCATION_CODE: "WAREHOUSE",
                LOCATION_CODE_NO: 1,
                LOCATION_DESC: "WAREHOUSE",
                DEFAULT_FLAG: "Y",
              },
              {
                LOGIN_NAME: "soban",
                LOCATION_CODE: "BTP",
                LOCATION_CODE_NO: 70,
                LOCATION_DESC: "BTP",
                DEFAULT_FLAG: "N",
              },
            ],
          },
        },
      },
    },
  },
};

function objToLowerCase(obj) {
  const newObj = {};
  Object.entries(obj).forEach(([key, value]) => {
  const newKey = key.toLowerCase().split('_').join('');
  if(typeof value !== 'object') {
  newObj[newKey] = value;
  } else {  
  newObj[newKey] = objToLowerCase(value)
  }
  });
  return newObj;
}
document.getElementById("p1").innerHTML = JSON.stringify(objToLowerCase(resp), null, 2)