Your workspace ID (this appears as app _id in your code) is a unique code assigned to your app when you create it in Intercom. There are a few ways you can find your workspace ID.
The easiest way to find your workspace ID is to check the URL of any page you have open in Intercom. It's the code that comes after apps/ in the URL. So for this example workspace, if we check the URL we can see that the workspace ID is gkeb4bs.
Your workspace ID is also available under Settings > Installation > Web in the "With code" tab: