Right click on any control in the pre section or in the channel strip in Cubase. Assign a quick control slot. Put the CC121 in quick control mode (press eq type and all bypass together). The EQ knobs now control the assigned controls in the channel strip.
Second way is hover over the control you want to move and move the A1 knob. The A1 knob now moves the assigned control. The first method is best as the quick control set ups can be saved.