根据选项选择更新数据库

I can't figure out what is wrong with my code.I'm new in php so can someone please tell me what am I doing wrong??

This is the form:

<center><br/><h2>Update Form</h2></center>
<div id="login">
    <fieldset>
        <legend><h3>Update Form</h3></legend>
<h4 style="color:pink;"><?php global $nam; echo $nam;?> </h4> 
<?php global $error; echo $error;?>                  
        <!-- the login form-->
<form action='login_reg_action.php' method='post' id='myform'>
            <div class="login">
            <table width="400px">

<tr>
<td><label>Username</label></td>
<td colspan="2"><span class="style8">
 <div align="center">
      <?php
      include 'connection.php';
      $sql = 'SELECT * FROM login_1 ORDER BY username';
      $sele=mysqli_query($conn,$sql);
      ?>
      <select name="login_id" style="width:250px; height:34px; border:1px solid #336666;">
        <option required="required" value="000" > [SELECT STUDENT]</option>
        <?php
       while($numu=mysqli_fetch_array($sele))
       {
      ?>
        <option required="required" value="<?php echo $numu['login_id'];?> ">  <?php echo $numu["login_id"];echo'  -  ';echo $numu["username"] ?>   </option>
        <?php
      }
      ?>
      </select>
      </label>
      </div>
  </td>

  </tr>
  <tr>
 <td><label>Rank</label></td>
 <td><select name="rank" id="rank" style="width:250px; height:34px; border:1px solid #336666;">
 <option value="000">Choose user rank</option>
 <option value="student">Student</option>
 <option value="candidate">Candidate</option>
 <option value="administrator">Administrator</option>
 </select></td>
 </tr>
 <tr><td colspan="2" align="left"><input type="submit" name="submit" value="Update" style="width:100px; height:34px; border:1px solid #336666; border-radius:4px;"></td></tr>
             </table>
            </div>
 </form>

and this the form action. This form will process any input data in the first form:

 <?php

 $servername="localhost";
 $username="root";
 $password="";
 $dbname="o-voting_db";
 //Create connection
 $con=mysqli_connect($servername,$username,$password,$dbname);


 $name      = $_POST['login_id'];
 $rank      = $_POST['rank'];



 if(!$name || !$rank){
 $error="Please fill empty fields";
 include"login_reg.php";
 exit();
 }
if(isset($_POST['submit'])) {
$sql1="UPDATE login_1 SET rank='$rank' WHERE username='$name'";


  // if($rank=='candidate'){
   //include 'reg_cand.php';
   //}

 $result = mysqli_query($con,$sql1)or die(mysqli_error($sql1));

 if(!$result){
 die("Could not update data: " .mysqli_error($con));
  }
 else{
 $nam="<center><h4><font color='#00FF00'>Successful update,</h4></center>  </font>";
include "login_reg.php";
}
}


?>