Is downloading channels that may contain inappropriate material onto a friend's receiver considered an ongoing sin, and what is the method of repentance from it if it is?

Allah commanded us to cooperate in righteousness and piety, and He forbade us from cooperating in sin and aggression. It is not permissible for a Muslim to aid in a sin or in anything that involves sin. Whoever aids in evil is a participant in the sin and bears a burden similar to it.

Sincere repentance erases what came before it, and one who repents from a sin is like one who has no sin. Part of complete repentance is to strive to remove and delete corrupt channels and to advise those who were previously helped. If effort is made towards reform and what can be reformed is reformed, then one has fulfilled their obligation.