How to change date format in PHP Codeigniter?

<?php
defined('BASEPATH') OR exit('No direct script access allowed');
class Change_Date_Format extends CI_Controller {
public function __construct() {
parent::__construct();
//$this->load->database();

}


public function index()
{
//$sampleDate = '2019-01-02';
$sampleDate = date("Y-m-d");
$convertDate = date("d-m-Y", strtotime($sampleDate));

print_r($convertDate);
}


}

if(!function_exists('changeDateFormat'))
{
function changeDateFormat($format = 'd-m-Y', $originalDate)
{
return date($format, strtotime($originalDate));
}
}

<?php
echo changeDateFormat('d-m-Y',$user->created_at)
?>

if ( ! defined('BASEPATH')) exit('No direct script access allowed');
date_default_timezone_set('Asia/Kolkata');


If you are looking globabally setup timezone in whole project then you can setup it CI application/config.php file

$config['time_reference'] = 'Asia/Dubai';

Add this line to autoload.php in the application folder:
$autoload['time_zone'] = date_default_timezone_set('Asia/Kolkata');

<?php defined('BASEPATH') OR exit('no direct script access allowed');
class Datedemo extends CI_Controller
{
public function __construct()
{
parent::__construct();
}

public function index()
{
$this->load->view('datetime');

}

public function insertdata()
{

date_default_timezone_set('Asia/Kolkata');
//$date = date('Y-m-d h:i:s');
$date = date("d-m-Y H:i:s");
//$time = time('H:i:s');

//echo date('h:i:s a m/d/Y', strtotime($date));
$time = date('h:i:s a', strtotime($date));

$data = array(
'date' => $date,
'time' => $time
);


$result = $this->Auth_model->datainsert($data);
}


}

<td> <?php

if(date('Y-m-d') == date('Y-m-d',strtotime($row->created_at))){

echo date('h:i A',strtotime($row->created_at));

}else{

//echo $row->created_at !="" && $row->created_at !="0000-00-00 00:00:00" ? date('d/m/Y h:i A',strtotime($row->created_at)):'';
echo date('d/m/Y h:i A',strtotime($row->created_at));
}
?></td>