It is obligatory to repent and ask the wronged person(s) for forgiveness
Q : I was ignorant and then Allah (Exalted be He) guided me to Islam. In the past, I committed some injustices and errors. I heard the Hadith of the Prophet (peace be upon him) that states: "He who has done a wrong affecting his brother's honor or anything else, let him ask for his forgiveness today before the time (i.e. the Day of Resurrection) when he will have neither a dinar nor a dirham." What should I do in this case?
A : Allah (Exalted be He) allows His Servants to repent of all sins. Allah (Exalted be He) says:
And all of you beg Allâh to forgive you all, O believers, that you may be successful
O you who believe! Turn to Allâh with sincere repentance!
And verily, I am indeed forgiving to him who repents, believes (in My Oneness, and associates none in worship with Me) and does righteous good deeds, and then remains constant in doing them, (till his death).
He who repents of his sins is like the one who has not committed a sin.
Anyone who commits a sin should hasten to repent, regret, give up the sin, and be truly determined not to return to this sin to show honor to Allah (may He be Praised), devote himself to Him, and fear His Punishment. Allah (Exalted be He) accepts the repentance of those who repent. When a servant observes sincere Tawbah (repentance to Allah), regrets what he did, and determines not to return to his sins for the Sake of and for Fear of Allah (Glorified and Exalted be He), He will forgive him and blot out his past sins, because of His Favor and Kindness. Nevertheless, if the sin is against people, the repentant person should give back the rights to their respective owners or ask for their forgiveness, such as saying, "My brother, forgive me," or "Pardon me", and repent for what he did. He must also regret it and determine not to do it again. This is based upon the Hadith you mentioned:
Whoever has wronged his brother, should ask for his pardon in this world (before his death), as (in the Hereafter) there will be neither a dinar nor a dirham. (He should secure pardon in this life) before some of his good deeds are taken and paid to his brother and if he has done no good deeds, some of the bad deeds of his brother will be taken to be loaded on him (in the Hereafter).
(Related by AlBukhari in his Sahih)
A Mu'min (believer) should be keen to free himself from his brother's right by giving it back to him or by asking for his pardon. If someone violates the honor of someone else, they should ask for forgiveness if possible. Otherwise, if the repentant person is afraid of the consequences or harm of informing the wronged party, he should ask Allah's Forgiveness for him, supplicate Allah for him, and mention his merits instead of the evils he mentioned about him in the same gathering in which he backbit him in the past. He should wash the bad deed away with good deeds by mentioning and speaking about the merits of the wronged man and asking Allah's Forgiveness for him. May Allah grant us success!