[tzs]

Or "the key that has the word 'command' printed on it" or "the key one left of the space bar" or "the key one right of the space bar".

Or, if their Mac supports "Hey Siri" and it is enabled, "Hey Siri, Open Bluetooth File Exchange".

[cassianoleal]

Or, you know... just show them in the camera since they're still on Zoom.