To begin with it's always best to test your original consoles sound works. It isn't always required, as you have have a dead speaker, but if your console works first its a good sign.
STEP 1. Open up the Game Boy Pocket using a Triwing screwdriver by removing the 6 screws on the back (2 inside the battery compartment).
STEP 2. Once inside, it is easier to also remove the main circuit board from the shell by removing the 3 philips screws from the bottom half. Before lifting out the console, push the white tabs on either side of the ribbon connector at the top towards the top of the shell. This releases the pressure on the ribbon cable and you can pull out the cable, leaving the screen stuck down in the front shell. Now remove the circuit board from the shell.
STEP 3. Remove the old speaker from the front PCB by cutting or desoldering the speaker wires.
STEP 4. Use double sided tape (optional) to secure the CleanAmp onto the back side of the speaker, as shown.
STEP 5. Take some wire (30awg or 28awg gauge wire - the thin stuff), cut it to length and solder the wires from the points on the Game Boy Color to the pads on the CleanAmp as shown.
STEP 6. Be careful when soldering the CleanAmp pads that you do not short the pads together or remove the resistors or capacitors near the pads.
STEP 7. Solder the two top right wires on of the CleanAmp to the speaker. Polarity doesn't matter, you can solder either wire to either side.