Post array from HTML form, and use results to update multiple rows in a mysql table

So I have this basic html form. My goal is to pass the values submitted to this form into a mysql table.

 <form action="?action=settings" method="post">
      <ul>
        <li>
           <label for="settingValue[1]">Setting 1:</label>
           <input type="text" name="settingValue[1]" id="setting1" required />
        </li>
        <li>
            <label for="settingValue[2]">Setting 2:</label><br>
            <input checked type="radio" name="settingValue[2]" value="1" />On<br>
            <input type="radio" name="settingValue[2]" value="0" />Off
         </li>
         <li>
             <input type="submit" name="saveChanges" value="Save Changes" />
         </li>
       </ul>
   </form>

My mysql table has only 3 columns (id, settingName, settingValue) So I want to update multiple records in my table using this form (In this case rows 1 and 2) by storing the value into the "settingValue" column.

After some research I found that what seems to be the best way to do this would be by posting an array (Which is what I attempted to do above), then use a foreach loop to to run through the array and update the table.

I guess my main problem is figuring out how to use the array. Because I need to UPDATE a record NOT create a new one. I also need to retain the ID so I can update the corresponding record.

After hours of googling my best guess was to do this:

if ( isset( $_POST['saveChanges'])) {
    foreach($_POST['settingValue'] as $key => $settingValue )  {
        $conn = new PDO( DB_DSN, DB_USERNAME, DB_PASSWORD );
        $conn->exec("UPDATE settings SET settingValue=$settingValue WHERE id=$key");
        $conn = null;
    }

But it is yielding no results.