How to creat update function of php

<?php
 define('DB_SERVER', 'localhost');  
 define('DB_USERNAME', 'root');
 define('DB_PASSWORD', '');
 define('DB_DATABASE', 'student_db');
 
 
 
 define('PROJECT_NAME','Student Tutorial');
 define('SERVER_NAME','localhost');


class DB_Class
{
    function __construct()
    {
        $connection = mysqli_connect(DB_SERVER, DB_USERNAME, DB_PASSWORD,DB_DATABASE) or die('Oops connection error -> ' . mysqli_connect_error());
    }
}
$connection = mysqli_connect(DB_SERVER, DB_USERNAME, DB_PASSWORD,DB_DATABASE) or die('Oops connection error -> ' . mysqli_connect_error());

/**********************General WebSite Settings************************************/
date_default_timezone_set("UTC");
?>

<?php
public $dbcon;
class Dbfunctions{
    
    public function __construct(){      
        $this->dbcon = mysqli_connect(DB_SERVER, DB_USERNAME, DB_PASSWORD,DB_DATABASE) or die('Oops connection error -> ' . mysqli_connect_error());                                
    }
    /* UPDATE FUNCTION */
    public function updateTable($tblName,$string, $condition){
		$condition = " WHERE " . $condition;
	   	$sql="UPDATE " . $tblName . " SET " .  $string . $condition;
		$sql."<br>";/* exit; */
	   	$rs= mysqli_query($this->dbcon,$sql);
        return true;
	}
}
?>