How to select strokes over multiple cells?

I want to do my clean animation above my rough animation… So i duplicated the rough layer to keep the same exposure…

Now i want to delete all the strokes on my duplicate… i am now doing this each cell, which is time consuming.
Is there a way to select over multiple cells? I thought that this ‘‘apply to multiple drawings’’ would do that, but i haven’t succeed to make that work… so i suppose that that is for something else? i don’t understand it.

Thanks in advance.