If you have not changed any of the defaults, you can open the Window Manager from the Start menu. Down near the bottom are three custom icons with a blue background. Click the one that looks like a window. You can also find the same icon on the Experience bar next to the EQII Start button, whenever the Command Bar (11 icons) is selected.
If you want to open the Window Manager to a specific setup page, there is usually a gold button with a blue gem in the upper left-hand corner of customizable windows. For windows that have a titlebar, the button will appear alongside the other frame buttons.