How to acess Private function of another class in PHP

I have a dbHandeller.php file . as follow

class dbHandeler {

    var $conn;

 public function __construct(){

        $this->initiatedb();

 }

    private function initiatedb(){

        //Details of the Databse
            $servername = "localhost";
            $username = "root";
            $password = "";
            $dbname = "xxxxxx";

            // Create connection
            $this->conn = mysqli_connect($servername, $username, $password, $dbname);

            // Check connection
            if (!$this->conn) {
                die("Connection failed: " . mysqli_connect_error());
            }else
               return $this->conn;

    }

 private function sql_query($query){

 }

}

Then I have donation.php and it extends the DB class

function __autoload($class_name) {
    include $class_name . '.php';
}

class donation extends dbHandeler{


    public function __construct(){

        $dbObj = new dbHandeler();
        $dbObj->initiatedb();
    }

    public function putDonation(){
        var_dump($_POST);

    }

    public function getDonation(){


    }
}

When I try to access the donation class I am getting following error

Fatal error: Call to private method dbHandeler::initiatedb() from context 'donation' in C:\xampp\htdocs\templeform\api\donation.php on line 13

error