//FORM
<input type="text" value="<?php echo $b['nis']; ?>" class="form-control" name="pass"
<input type="text" value="<?php echo $b['id_siswa']; ?>" class="form-control" name="id" >
<input type="submit"  onclick="return confirm('Reset Password ?')"; name="reset" value="Reset" class="btn btn-warning ">
	</td>
     </tr>
</table>
<?php
if (isset($_POST['reset'])) {
$siswa->reset($_POST['pass'],$_POST['id']);
//echo "<script>alert('Password Telah Direset');</script>";
print_r($_POST);
}
 ?>

//CLASS
class siswa
{
    function reset($pass,$id)
    {
        $pass = md5($pass);
        mysql_query("UPDATE siswa SET password = '$pass' WHERE id_siswa='$id' ");
    }