How can one atone for buying a laptop for someone who uses it to watch theḥarām (forbidden things) of the village, given the difficulty of advising him due to his old age?

Assisting in disobedience to Allah is forbidden, as Allah Almighty says: "And do not cooperate in sin and aggression." If it is highly probable that the buyer will use the device for a forbidden purpose, then it is not permissible to sell it to him. As for what has passed, one must repent from it by feeling remorse and resolving not to return to it, and advise the person not to use the device for forbidden acts, and clarify the ruling on that. After that, its use for disobedience does not cause harm, and no sin befalls the adviser.