I want to repent from backbiting. Because now I regret for what I've done and I fear the punishments in the afterlife. I was teenager when I committed the sins. Now, I'm trying to apologize everyone whom I've wrong but some of them I can't contact them or I didn't remember that have I wronged them or not. I feel very bad :( What should I do and What can I do?
Narrated from Abu Huraira: that he heard the Prophet (ﷺ) saying, "O Allah! If I should ever abuse a believer, please let that be a means of bringing him near to You on the Day of Resurrection. (اللَّهُمَّ فَأَيُّمَا مُؤْمِنٍ سَبَبْتُهُ فَاجْعَلْ ذَلِكَ لَهُ قُرْبَةً إِلَيْكَ يَوْمَ الْقِيَامَةِ)" in Sahih al-Bukhari (6361)
As you see, you make Du’a for those that you can not reach to apologise to. This is a general du‘a, but of course you can also phrase it in your own words if this is difficult for you to utter. Make supplications that Allah should reward all of them whom you wronged with Jannatul Firdaus, that their sins should be forgiven and that they should be rewarded in this and the next life (for example).
Shaykhul-Islam Ibn Taymiyah said: "Whoever wrongs a person by slandering him, backbiting about him or insulting him, then repents, Allah will accept his repentance, but if the one who was wronged finds out about that, he has the right to settle the score. But if he slandered him or backbit about him and the person did not hear of that, then there are two views according to the scholars, both of which were narrated from Ahmad, the more correct of which is that he should not tell him that he spoke against him in his absence. It was said that he should rather speak well of him in his absence just as he spoke badly of him in his absence, as al-Hasan al-Basri said: the expiation for gheebah is to pray for forgiveness for the person about whom you backbite." Majmu’ al-Fatawa (3/291)