how to retrieve the product id based on the selected id_item

public function store(Request $request)
    {
        DB::beginTransaction();
        try {
            $save = new Service;
            $save->name = $request->name;
            $save->product_treatment_code = $request->product_treatment_code;
            $save->description = $request->description;
            $save->save();

            $items   = [];
            foreach ($request->items as $r) {
                $dummy  = new ServiceDetail;
                $dummy->item_id     = $r['item_id'];
                $dummy->product_id  = $r['product_id'];
                $dummy->expire_date = $r['expire_date'];
                $dummy->uom_id      = $r['uom_id'];
                $dummy->price       = $r['price'] ? $r['price'] : 0;
                $dummy->qty         = $r['qty'] ? $r['qty'] : 0;

                $items[] = $dummy;
            }
            $save->service_details()->saveMany($items);
            DB::commit();
        }catch(\Exception $e){
            DB::rollback();

            return response()->json([
                'code' => 500,
                'error' => 'Can not save the data'
            ], 500);
        }
    }

 $product = Item::where('id_item', $id)->where('id_item', $id)->firstOrFail();

so automatically retrieve product id data when any items that I choose and input into the column array