A police report cannot be dropped once it's been made. However, if you wish to drop the charges that were filed because of your police report, you may or may not be successful. The police department may refuse to drop the charges because of the severity of the crime.
Contact the law enforcement agency where you made the report. Explain that you know that you can't revoke a police report, but that you'd like to drop the charges against the offender. The police cannot drop charges against the offender, but they can note the fact that you're asking for them to be dropped.
Meet with the district attorney, if one has been assigned to the case. Explain to her why you'd like the charges dropped. If you believe that you've made an error or that the wrong person has been charged, show her any evidence that supports your claim. The state may still decide to press charges against the offender despite your wishes, however.
Present your evidence and testimony to the defendant's attorney if the state continues to press charges on your behalf. Be prepared to testify. If the state believes that it has enough evidence against the defendant to continue with the case despite your wish to drop the charges, the defendant will need your testimony to have a chance at acquittal.