This is how you manually control Stewy. The KY-023 is a PS2-style analog joystick with two 10k potentiometers for X and Y axis movement, plus a push-button when you press straight down.

It connects to the head PCB with a 5-pin JST-XH cable and mounts on a printed standoff inside the head enclosure. Works at 3.3V or 5V and outputs analog signals on the VRx and VRy pins.