If you want to filter a shortcode by Organizer ID you need to find the internal ID assigned by Eventbrite. Unfortunately this does require a few steps, but straightforward if you follow the instructions

• Find your Organization ID ( not Organizer! ) by following this guide
• List your Events as seen by the API by following this guide

Then scroll down the results ( or use ctrl-f organizer_id ) to find the id associate with an Event. You may find the API Explorer filters on the right useful to find different Events for different organizers.