Step 2: Exploration
Unscrew the 6 (or so) screws on the back of the plaque. The back half should come off fairly easily, but BEWARE: there are several very important wires running from the back to the front half, and to disconnect them would surely cause some grief.
Take a look at the circuit board. Many of the solder points connect to the motor mechanisms that make the bugger flop around. The specific area you are looking for is where the IC (really just another PCB soldered in at a right angle to the main PCB) connects to the board. There is a row of rectangular solder points: this is your goal.
Locate points A, B, and C on the board. These are the points you will be soldering to to make the main bends.
Also, there is a photocell already in the the front half; it's that thing that makes the fish go off every time you walk by it, hidden in a little pit under the red button on the front. Locate this on the inside, as this will be instrumental in the coolness of the completed project.