If we had the Beis ha Mikdash now and someone wants to bring a korban for the sin of bad thoughts or zera le batala, should he bring a chattah offering or shelamim or olah for kapparah?
A korban chattas is only brought for a sin that was done mistakenly, which carries the punishment of karet if it was done on purpose, (such as chillul Shabbos). A korban olah is brought can be brought for the sin of not performing a positive commandment or even a negative one that is followed by a positive one, (the positive one serves as a kapara for the negative one). Although zera levatala is a serious sin, I am not sure if any specific korban would be applicable. Nevertheless, a person can do teshuva, even nowadays by working on being more careful with his thoughts and mainly by adding to his torah study.