Source flip book for sprite component will not change

I have followed this tutorial (Paper 2D #5 - Top Down Character Full Process - Unreal Engine 4 - YouTube ) almost exactly step by step, simply using a different map, and different sprites to make a different set of character flip books, but when I get to 15:35, where he chooses his source flip book in the viewport of NewCharacter, I select the flip book I’d like as my “idle” and nothing happens. The drop down menu closes, but the source flip book still says none. I don’t know what to do. Please help, thank you.