Advice for reporting sexual or other forms of harassment is available on the website of the Committee on the Status of Women in Astronomy (CSWA). Here is a summary of the more detailed information available on the CSWA website:
Write everything down (times, places, nature of the incident, and comments made). Save emails, notes, etc. Tell someone you trust. It is likely that you will have to write and sign an official letter of complaint, documenting the nature of the harassment and/or discrimination. Be as detailed as possible. Supporting documentation and statements from witnesses should be submitted with your letter.
Any individual covered by this policy who believes that he or she has been subjected to harassment should complete the online reporting form to submit the incident for review. All complaints will be treated seriously and be investigated promptly. Confidentiality will be honored to the extent permitted as long as the rights of others are not compromised.