What are the wrongs committed against people, and how can atonement be made for them and restitution returned to their rightful owners, especially if they are due to slips of the tongue and are not material?

Repentance from sins related to the rights of people requires seeking their forgiveness. If a person forgets the injustices he committed against others, yet is sincere in seeking their forgiveness should he remember them, it is hoped that Allah will absolve him of these sins. He must supplicate and seek forgiveness for those he wronged and ask Allah to absolve him of these rights. General repentance, by Allah's will, forgives all sins, even those a person has forgotten, unless there is an impediment that necessitates specificity.