<td class="align-middle text-center dropdown">
 <button type="button" class="btn btn-secondary dropdown-toggle" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">選択してください</button>
  <div class="dropdown-menu" aria-labelledby="dropdown1">
   <a class="dropdown-item" href="">選択肢A</a>
   <a class="dropdown-item" href="">選択肢B</a>
   <a class="dropdown-item" href="">選択肢C</a>
  </div>
</td>

...
public function index(Request $request)
{
 $Check = $this->washRepository->save();
 return ['Check'=>$Check];
}
...

...
/**
 * 登録
 * 
 * @param CheckStatus $check_status
 */
public function save($check_status)
{
 $em = $this->getEntityManager();
 $em->persist($check_status);
 $em->flush($check_status);    
}
...