<form action="{{action('CuentaController@asignar')}}" method="post">
<select name="valor" id="valor" class=" form-control" value="{{ old('tipo') }}" required>
@foreach($usuariosOpciones as $user_id => $usuario_ad)
<option value="{{ $user_id }}">{{ $usuario_ad }}</option>
@endforeach
</select>
{{csrf_field()}}
<button class="btn btn-danger btn-xs" type="submit"><span class="glyphicon glyphicon-plus-sign"></span></button>
</form>