// $twitter_check represents the field from the database which equals 'Yes' or 'No'

<label class="switch">
  <input type="checkbox" name="check-twitter" <?php echo $twitter_check == 'Yes'?'checked':''; ?>>
  <div class="slider"></div>
</label>

if(isset($_POST['check-twitter']) && $twitter_check == "No"){
    //SQL UPDATE $twitter_check = 'Yes'
    } elseif(isset($_POST['check-twitter']) && $twitter_check == "Yes") {
    //SQL UPDATE $twitter_check = 'No'
    }

<input class="button" type="submit" name="submit" value="Save"/>