If one has uttered a potentially harmful statement about someone, he has committed a n that is both bein adam la’Makom, between man and Hashem, and bein adam la;chaveiro, between man d his fellow. Confession, regret and resolution for the future can only serve as teshuvah for one’s sins before Hashem. For sins against man, one must approach the person and beg forgiveness.
This only applies to a situation where one’s speech has already caused damage. If a potentially damaging statement was made but no actual harm has resulted as of yet, it is the speaker’s responsibility to do his best to prevent this from happening.
A practical way of accomplishing this would be to approach anyone who has heard the harmful information, and explain that it was inaccurate.
Sefer Chofetz Chaim, 27 Tishrei, page 102