How to save sortable select2 options ?

Here at my blade file , I'm trying to make this select2 option menu sortable

<select class="form-control select2" name="selected_items[]" multiple="multiple">
    <?php $default = null; ?>
    @if(isset($items))
        @if (! empty($selectedValues))
            @foreach($selectedValues as $selectedVal)
                @foreach($items as $option)
                    @if ( $selectedVal == $option->$itemId )
                        <option value="{{ $option->$itemId }}" selected="selected">{{ $option->$itemTitle }} {{ $option->slug ? '(' . $option->slug. ')' : '' }}</option>
                    @endif
                @endforeach
            @endforeach
            @foreach($items as $option)
                @if ( ! in_array($option->$itemId, $selectedValues) )
                    <option value="{{ $option->$itemId }}">{{ $option->$itemTitle }} {{ $option->slug ? '(' . $option->slug. ')' : '' }}</option>
                @endif
            @endforeach
        @else
            @foreach($items as $option)
                <option value="{{ $option->$itemId }}">{{ $option->$itemTitle }} {{ $option->slug ? '(' . $option->slug. ')' : '' }}</option>
            @endforeach
        @endif
    @endif
</select>

I used the following JS to make it draggable

            var el = document.querySelector('.select2-selection__rendered');
            Sortable.create(el, {})

Right now it's sortable , but it doesn't save. what should I do so when I click on save the reordered values get saved?