how to adopt a new icon (created via icon composer) into my app?

To adopt a new icon created via Icon Composer into your app, follow these steps:

Create and Export the Icon: Use Icon Composer to design your icon. You can start by importing vector content and organizing layers for different rendering modes. Once you're satisfied with your design, export the icon file.
Integrate with Xcode: Drag the exported icon file into Xcode. In Xcode, go to the Project Editor and select your new icon as the app icon.
Build and Run: After setting the icon in Xcode, build and run your app to see how the icon adjusts to different platforms and appearances.

For more detailed guidance, you can refer to the session Create icons with Icon Composer (13:16) which covers the delivery process of integrating icons into your app.