allo/app/Http/Controllers/Controller.php

<?php

namespace App\Http\Controllers;

use App\Model\Form;
use App\Model\WorkOrder;
use Illuminate\Foundation\Bus\DispatchesJobs;
use Illuminate\Routing\Controller as BaseController;
use Illuminate\Foundation\Validation\ValidatesRequests;
use Illuminate\Foundation\Auth\Access\AuthorizesRequests;

class Controller extends BaseController
{
    use AuthorizesRequests, DispatchesJobs, ValidatesRequests;

    public function getUntaggedWorkOrder()
    {

        $result = array();
        $work_order = WorkOrder::all();

        foreach ($work_order as $key => $a) {
            $untaggedform = Form::where('_id',$a->_id)->where('customer_category',null)->get();

            dd($untaggedform);
                array_push($result, array(
                    '_id' => $untaggedform->_id,
                ));
        }

        return json_encode($result);
    }
}