How to access to "sub" icons ?

Hello to all,

I have customized the drawing iconbar (called draw toolbar in the getting started guide) in order to have the possibility for example to choose when I draw a circle whether I indicate center, radius, diameter or other options (like in draw menu). Till here, everything is ok ; there is a small black downward arrow in the bottom right corner of the icon (circle). My problem is that I don't know how to access to the "sub" icons , I tried with holding "alt", "ctrl" keys but without success, how should I do ?

Thanks in advance for your help

Thomas