How can one be absolved from injustices related to people's rights, especially when it is not possible to identify the individuals or the nature of the harm, and is it sufficient to supplicate, give charity, or make indirect contact? What are the consequences of the wronged forgiving or not forgiving in this world and the hereafter?

Repaying injustices is an Islamic obligation and a condition for repentance concerning the rights of people. If the injustices are material, return the goods to their owners or ask for their forgiveness. As for backbiting, you should frequently pray for and seek forgiveness for those you backbit. Give charity on their behalf if it is difficult to know or meet them. Assault with the hand necessitates asking for forgiveness or enabling the wronged person to take retribution. The wronged person is not obligated to forgive, but forgiveness is better, for Allah Almighty has commanded pardon and promised great reward for it.