What is the way to atone for the sins of oppressing people, especially if the oppressor cannot reach the wronged person to ask for forgiveness or to appease them?

The nature of the injustice was not mentioned, but oppressing people by taking their money, shedding their blood, violating their honor, slandering and insulting them, beating them, or assaulting them in any way, is considered a grave sin for which Allah has promised a severe punishment, as confirmed by His saying, "And whoever among you commits injustice, We will make him taste a great punishment," and His saying, "Indeed, for the wrongdoers there is a painful punishment." In the Hadith (definition): "Whoever wrongs by a span of land, it will be a collar around his neck from seven earths," and "A believer will continue to be in a state of ease concerning his religion as long as he does not shed unlawful blood." The oppressor must repent sincerely and restore rights to their owners, whether by returning money, paying blood money or compensation, or appeasing the wronged party. This is the only way to expiate sins related to the rights of people. He must also continue to search for the rightful owner if he believes he can reach him, and frequently seek forgiveness, perform good deeds, and give charity.