In accordance with clause 1 part 1 of article 5 of the Law of Ukraine "On the State Bureau of Investigation" No. 794-VIII dated 12.11.2015, the State Bureau of Investigation solves the tasks of prevention, detection, termination, disclosure and investigation of crimes committed, including by employees law enforcement agencies.
Therefore, you need to submit a statement about the commission of a criminal offense by police officers to the State Bureau of Investigation. Here is a convenient form on the DBR website, where you can submit a relevant application - https://dbr.gov.ua/pov-crime