I want to repent from backbiting. but I can't remember whom I was wronged to. What should I do?

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?