Praise be to Allah.
Allaah has enjoined repentance upon His slaves, as He says (interpretation of the meanings):
“And all of you beg Allaah to forgive you all, O believers, that you may be successful”
“O you who believe! Turn to Allaah 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)”
And the Prophet (peace and blessings of Allaah be upon him) said: “The one who repents from sin is like one who has never sinned.”
Whoever commits any sin must repent, regret what he has done, give it up, keep away from it and resolve not to go back to it. Allaah accepts the repentance of those who repent.
When a person sincerely repents by regretting what he has done and resolving not to repeat it, and he gives it up out of respect and fear of Allaah, then Allaah accepts his repentance and wipes out his past sins by His grace and kindness.
But if the sin involved wrongdoing against someone else, then the sinner has to do what he is obliged to do by repenting from what has happened, regretting it, giving it up and resolving not to do it again. He must also restore the rights of the one whom he wronged, or seek his forgiveness , such as saying, Please forgive me,” etc. Or he should give him his dues, because of the hadeeth quoted in the question, or other ahaadeeth and aayahs. The Messenger (peace and blessings of Allaah be upon him) said: “Whoever has done some wrong to his brother, let him seek his forgiveness today before there is no dinar or dirham, when if he has some righteous deeds (to his credit), some of his hasanaat (good deeds) will be taken in proportion to his wrongdoing, and if he has no hasanaat some of the sayi’aat (bad deeds) of the one whom he wronged will be taken and added to his burden.” (Narrated by al-Bukhaari in his Saheeh). So the believer should strive to put things right and restore his brother’s rights. So he should either give him his dues or ask him for his forgiveness. If it has to do with his honour then he has to ask for his forgiveness if he can. If he cannot, or he fears the consequences of telling him or that telling him about what he said will cause more trouble, then he should pray for forgiveness for him and make du’aa’ for him, and mention his good points that he knows of , to compensate for saying bad things, aiming to wash away something bad with something good. So he should speak of his good points that he knows of and spread good words about him to counteract the bad things which he said before, and he should pray for forgiveness for him and make du’aa’ for him. In this way the problem will be solved.