Remove the old cable.

Make sure your new mouse cable has a 5-pin molex connector that is compatible with the Razer Viper's PCB.

Route the cable through the previous route that the original cable was in, remembering to press down with your Phillips #0 screwdriver so the PCB can fit nicely on top.

Lastly, plug the molex power connector of the new cable back into the PCB of the Razer Viper Mini and make sure it is tightly fitted.