What must one who unwittingly initiated a bad practice do to disavow themselves of its sin and the sin of those who acted upon it?

Whoever commits a sin by mistake, unintentionally, incurs no sin, for Allah Almighty says: "And there is no blame upon you for that in which you have erred, but [only for] what your hearts intended." As for whoever intentionally commits a sin and establishes a bad precedent, it is obligatory for him to repent to Allah and strive to remove the evil he has done. If he is unable, then Allah does not burden a soul beyond its capacity, and it is hoped that Allah will not hold him accountable for what others do after his repentance.