As in the rest of Cubase VST, you can use the mouse to change any value in a value field or double click to enter it from the keyboard. But the IPS has some special fields whose values are indicated graphically like this:
To edit a value you can either drag in this area....
...or change this value
Here you can click and drag directly in the graphics to set a value. You can also set the value as usual (using the mouse or keyboard) in the small value field shown below the graphics.
If you hold down [Alt] you are changing the selected parameter in both IPS A and IPS B.