In OpenLP, go into Settings -> Configure Shortcuts.
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Go down to the Live Toolbar section and click the Next Slide (or Previous Slide) line.
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At the bottom alongside the Custom option, there are some buttons labelled Down/PgDown or Up/PgUp. Click the one you don't want to use when advancing with the keyboard.
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Then with the Bluetooth clicker, click the next slide button. The shortcut dialog should hopefully update the button label with whatever keypress the clicker sends.
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Then click OK.