<form action="" method="post" >
    <table width="700" border="0">
        <tr>
            <td align="left">  Current Password : </h3> </td>
            <td align="left"> <input class="form-control"  type="password" name="old_pass" required /></td>
        </tr>

        <tr>
            <td align="left">  Enter New Password : </h3> </td>
            <td align="left"> <input class="form-control"  type="password" name="new_pass" required /></td>
        </tr>

        <tr>
            <td align="left">  Confirm New Password: </h3> </td>
            <td align="left"> <input  class="form-control" type="password" name="new_pass_again" required /></td>
        </tr>

        <tr align="center">
            <td colspan="4"><br><input class="btn btn-success" type="submit" name="change_pass" value="Change Password"/></td>
        </tr>
    </table>
</form>

<?php
include("../includes/db.php");

    $current_user=$_SESSION['customer_email'];
    //validating password
    if(isset($_POST['change_pass'])) //if user clicks change pass
    {
        $old_pass=$_POST['old_pass'];

        $new_pass = $_POST['new_pass'];
        $new_pass_again=$_POST['new_pass_again'];

        //validating old password
        $get_real_pass="select * from customers where customer_pass='$old_pass'";
        $run_real_pass=mysqli_query($con,$get_real_pass);

        $check_pass=mysqli_num_rows($run_real_pass);

        if($check_pass==0)

        {
            echo "<script> alert('Invalid current password!')</script>";
            exit();
        }
        if($new_pass!=$new_pass_again)
        {
            echo "<script> alert('New password did not match!!')</script>";
            exit();
        }
        else
        {
            $update_pass="update customers set customer_pass='$new_pass' WHERE customer_email='$current_user'";

            $run_pass=mysqli_query($con,$update_pass);

            if($run_pass)
            {
                echo "<script> alert('Password changed successfully!')</script>";
                echo "<script>window.open('my_account.php','_self')</script>";
            }
            else
            {
                echo "<script> alert('Error occured!!!')</script>";
                echo "<script>window.open('my_account.php','_self')</script>";
            }
        }
    }
?>