How to trigger sysdiagnose if my Volume Down button is broken?
You can access this functionality through AssistiveTouch on your iPhone, which creates an on screen icon that replaces all the hardware functions of your device for device accessibility, however this is particularly useful when physical buttons on your device are broken.

This can be enabled by opening Settings &gt; General &gt; Accessibility &gt; AssistiveTouch, and turning on AssistiveTouch.

Then for your specific issue you can enable the Analytics option as a single or double tap option, a long press or 3D touch of the button that is brought up.