If you can apply for a waiver, the consular officer at the U.S. Embassy or Consulate where you applied will inform you how to apply.
Immigrant Visa and K Nonimmigrant Visa Applicants - If you can apply for a waiver, you must mail Form I-601, Application for Waiver of Grounds of Inadmissibility, directly to a U.S. Citizenship and Immigration Services (USCIS) Lockbox facility, with few exceptions. Learn more on the USCIS website