Should a technician fulfill a colleague's request to install sound drivers on his device, knowing that the colleague uses them to listen to music? And is fulfilling the request part of his job duty as the one responsible for device maintenance, or should he refuse it?

If you predominantly believe that this technology will be used for listening to forbidden things, then it is not permissible for you to assist him in it. This is because such assistance would be considered aiding him in sin, which is forbidden, as Allah Almighty says: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression." You should advise him, remind him of Allah, warn him of punishment, clarify the prohibition of listening to forbidden things, and guide him to listen to the Quran and purposeful nasheeds, and to entertain himself by reading books of the Sirah and stories of the righteous predecessors.