Is it permissible to repair an internet device – to be used for permissible and good purposes – knowing that others use it for forbidden things, and with my father’s command for me to repair it for a permissible purpose, even though he uses it via a pirated operating system?

There is no objection to installing internet cables for permissible uses, and the use of them by others for prohibited purposes does not cause harm as long as it cannot be prevented. Likewise, there is no objection to repairing the device for the father, even if he uses it via a cracked system.