How can I atone for the sin of backbiting and slander?

Gheebah (backbiting) and Nameemah (slanderous tale-bearing) are expiated by sincere repentance that fulfills its conditions, because Gheebah and Nameemah are among the most heinous sins. Repentance is obligatory for every sin, and its conditions are: to cease the disobedience, to regret committing it, and to resolve never to return to it. If the disobedience involves the right of a human being, then one must seek their forgiveness if possible, and if it does not lead to a greater mischief. If seeking forgiveness would lead to increased animosity, then one should seek forgiveness without detailing the offense, or mention them favorably and frequently seek forgiveness for them in the gatherings where one backbit them.