After you determine that something that happened was harassing, let that person know that you take issue with their behavior. If they don’t stop or if you’re afraid that saying something might negatively affect your career, you should share your feelings with your organization by following its procedures for reporting sexual harassment. They’re available on its website or in your employee handbook. In any case, you’ll have to talk to the manager or HR.
Never wait for too long, because the law allows reporting 180 days after the incident. Write a formal letter about the incident and hire an attorney if you experience retaliation.