If I accidentally spoke lashon hora about a group of people, to a group of people and I am unsure if this may have changed some of the views of this group (I tried to explain a behavior of a certain group but it could be seen as being derogatory), what do I have to do in order to do teshuva, do I have to go back and apologize to those people saying that I apologize it may have been lashon hora?
Thank you, tizku lmitzvot.
First of all, as you indeed wrote, speaking negatively about a group of people is considered lashon hora. Lashon Hora is not limited to speaking negatively about an individual (Chafetz Chaim 10:12)
It seems that nothing negative happened to the group of people that you spoke about as a result of what you said about them, nor were any of them insulted (because they do not know that you spoke negatively about them). If that is the case, you do not have to tell them that you spoke negatively about them, and in fact you should not tell them at all. In this case, teshuva between you and Hashem will suffice. This is explicit in Sefer Chafetz Chaim (4:12 and Be’er Mayim Chaim ibid 47,48).
If the negative words caused harm to the group of people that you spoke about, but they do not know that you are the one who caused them the harm- this is the topic of a well known machlokes between the Chafetz Chaim (ibid) and Rav Yisrael Salanter. When the Chafetz Chaim brought his Sefer to Rav Yisrael Salanter to receive Rav Yisrael’s haskama, Rav Yisrael took issue with the Chafetz Chaim’s opinion that one must ask forgiveness from the hurt party even when the hurt party does not know who caused them the damage. Rav Yisrael said that doing so will only cause friction to develop between the two parties and be a cause of additional pain. The minhag, as heard from HaRav Yisrael Gans shlita, follows the opinion of Rav Yisrael Salanter.
All the best