<?php
header("Access-Control-Allow-Origin: *");
// Initialize the session
session_start();
 
// Check if the user is logged in, otherwise redirect to login page
//if(!isset($_SESSION["loggedin"]) || $_SESSION["loggedin"] !== true){
//    header("location: login.php");
//    exit;
//}
$id=$_SESSION["uid"] ;
$username=$_SESSION["username"];                           
$guser=$_SESSION["guser"];
// Include config file
require_once "configs.php";
//if($_SERVER["REQUEST_METHOD"] == "POST"){
$username=trim($_POST["username"]);
$pid=trim($_POST["pid"]);
 // Validate password
    if(empty(trim($_POST["password"]))){
        $password_err = "Please enter a password.";     
echo $password_err;
    //        mysqli_stmt_close($stmt);
exit;
    } elseif(strlen(trim($_POST["password"])) < 2){
        $password_err = "Password must have atleast 2 characters.";
echo $password_err;
     //       mysqli_stmt_close($stmt);
exit;
    } else{
        $password = trim($_POST["password"]);
    }

if($_SERVER["REQUEST_METHOD"] == "POST"){
$username=trim($_POST["username"]);
      // Prepare a select statement
     //   $sql = "SELECT id FROM users WHERE id = ?";        
//$stmt = $db->prepare($sql);
    //        // Bind variables to the prepared statement as parameters
//  $stmt->bindParam(1,$param_id);    
            // Set parameters
    //        $param_id = $pid;            
            // Attempt to execute the prepared statement
 //        $stmt->execute();
        
//}

// Prepare an update statement
        $sql = "UPDATE users SET password = ? WHERE id = ?";
        
        $stmt = $db->prepare($sql);
            // Bind variables to the prepared statement as parameters
         $stmt->bindParam(1,$param_password);
             $stmt->bindParam(2,$param_pid);
            // Set parameters
            $param_password = $password;//password_hash($new_password, PASSWORD_DEFAULT);
//            $param_id = $_SESSION["id"];
  $param_pid=$pid;          
            // Attempt to execute the prepared statement
           $stmt->execute();
  echo "OK" ;            
//  echo "set new password to ".$param_username;
				session_destroy();
                
				//header("location: login.php");
                exit();
         
        }

Edit file:setpasswdn.php2550