Custom query with CakePHP3 REST API

I just finished this tutorial creating a REST API with cakePHP3:

http://www.bravo-kernel.com/2015/04/how-to-build-a-cakephp-3-rest-api-in-minutes/

Everything works perfectly and all results are delivered via json
(using postman). My question is, where do I edit/create my query so I
can limit the results based on id. I’m assuming I must do it
Model/Table/Cocktails.php? If so, then do I create a custom route to
that?