On my wheel anyways, the setting for high/low was unused and I had to assign it to a button so it may be the same for the DS4. On the screen that lets you remap the controller there is a box you can click on Down on the bottom right corner that will show all unassigned options if I remember correctly, or maybe is just shows all available options that can be assigned, the but high/low option is in there. There is also an option to just flash the lights in there a second well.
Edit: I was wrong, close, but still wrong lol. I just had unused buttons on my wheel that I was able to assign it too is all, but there is two options for lights for a DS4, Flash and toggle High/Low and just Toggle High Low, you can assign it to any button you wish.
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