I found they have select2 file in their vendor folder, so i linked them (those links works when i open these two files in web browser). in header
<link href="{{asset('adminbackend/vendors/select2/dist/css/select2.min.css')}}" rel="stylesheet">
in Footer
<script src="{{asset('adminbackend/vendors/select2/dist/js/select2.full.js')}}"></script>
in body
<div class="item form-group">
<select class="form-control select2-multi" name="tags[]">
@foreach($tags as $tag)
<option value="{{$tag->id}}"> {{$tag->name}} </option>
@endforeach
</select>
</div>
in body
<script type="text/javascript">
$(.select2-multi').select2();
</script>
but, still it not working.. this code found in here https://www.youtube.com/watch?v=BNUYaLWdR04&list=PLwAKR305CRO-Q90J---jXVzbOd4CDRbVx&index=43