Changing primary display without the display settings window

[Microsoft Windows]

I am using my laptop as a desktop with a connected monitor as the laptop screen is broken (has been for years) with the monitor as my primary display. However something seems to have gone wrong and now the laptop screen (dead) has reverted to being primary, and I can't change it as the 'display settings' window opens on the dead screen, so I can't find it... How do I change my display settings now?

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