Keynote presentations - how to make Keynote use only two of my three monitors?

Hi there

I have three monitors.

For a Keynote presentation, I want Keynote to use two monitors (1 for the slideshow, the 2nd for the presenter notes/next slide)... but I want to use the 3rd monitor to see my desktop/another app.

However, whenever I have 3 monitors plugged in, Keynote automatically uses all 3 monitors.

How can I have Keynote only use 2 monitors while presenting so i can use the 3rd for something else?

When I go to Play > Customize Presenter Display, I can see how to configure what to have from Keynote in each monitor, but not an option for any of the monitors to NOT be used by Keynote at all.

Hope this makes sense.

Thanks so much in advance for any advice, much appreciated.

Nicholas