Audio Tab

Welcome to the Zoom Community, @CarolB.

I can't tell exactly what you're looking at.  Can you provide a screen shot?

I also can't tell whether you're just trying to select a microphone, or if you're trying to enable Original Audio for Musicians.

If you open up the Settings screen on your Desktop app, there should be an Audio tab on the left side:

The yellow highlighted area is where you select the microphone, and the red-circled area is where Original Sound for Musicians is enabled and configured, but it still needs to be turned on vide the floating button on the Zoom Meeting application in the upper left corner:

You can also make mic and speaker selections directly from the Mute/Unmute button in the lower left corner of your Meeting window:

(You probably won't have as many devices listed!)