How to fetch particular data from api using php - php

Question

I am new in fetching data using APIs and need to fetch some particular columns data from a number of columns available. I am able to fetch all the data using API but wondering how to fetch particular columns. Below is my code:
<?php
$url = 'myurl';
$curl = curl_init();
curl_setopt_array($curl, array(
CURLOPT_URL => $url,
CURLOPT_RETURNTRANSFER => true,
CURLOPT_ENCODING => "",
CURLOPT_MAXREDIRS => 10,
CURLOPT_TIMEOUT => 30,
CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
CURLOPT_CUSTOMREQUEST => "POST",
CURLOPT_POSTFIELDS => "{\"username\": \"test\", \"password\": \"test\"}",
CURLOPT_HTTPHEADER => array(
"accept: application/json",
"cache-control: no-cache",
"content-type: application/json"
),
));
$response = curl_exec($curl);
$err = curl_error($curl);
curl_close($curl);
if ($err) {
echo "cURL Error #:" . $err;
} else {
echo $response;
}
$request = curl_init();
curl_setopt($request, CURLOPT_SSL_VERIFYPEER, FALSE);
curl_setopt($request, CURLOPT_RETURNTRANSFER, TRUE);
curl_setopt($request, CURLOPT_CUSTOMREQUEST, "POST");
curl_setopt($request, CURLOPT_HEADER, FALSE);
$result = curl_exec($request);
curl_close($request);
if ($result) {
$data = new SimpleXMLElement($result);
foreach ($data->Item as $entry) {
echo "XML Activity Name: " . $entry->ActivityName . "<br>";
}
} else {
exit();
}
?>