The window displaying Audio Device and Buffer Size selection can be found in the Ozone standalone application in the top menus under:
Window > Audio Devices (same for mac and PC)
Here, you can select any detected Audio Devices. If your device is missing, be sure your audio drivers for that are up to date and it's output is compatible with software sources such as Ozone.
You can also adjust your buffer size to adjust the time your CPU has to process audio processing, if you're having performance issues, you can see more information in our Help Documentation.