How can one definitively rid themselves of backbiting and atone for those who have been backbitten, while ensuring not to return to it?

Backbiting is forbidden in Islamic law. Whoever has backbitten must perform sincere repentance by refraining from it, regretting it, and resolving never to return to it, as well as by keeping away from those who backbite and from gatherings where backbiting occurs.

For someone who has backbitten individuals, they should ask them for forgiveness and pardon without explicitly stating what they said. If doing so would lead to greater harm, then they should supplicate for them and mention their good qualities.