I think that the thing you are calling a button is actually the little round window through which you are supposed to be able to see how full the rinse-aid dispenser is. (I find it difficult to tell anything by this window, though.) To add the rinse aid, you lift the tab (at one end of the rectangular piece that contains the round window) where it says "lift," and then pour the rinse aid into the receptacle where it says "Fill." When the rectangular piece is lifted, you can see a little round dial with a handle going across it that lets you control how much of the rinse aid gets dispensed each time. You might be mistaking that for a button as well.