Recently i fell down from bike and gone for mri of my right knee. the report says that "mild joint effusion". how do i overcome this problem..?

Ice, elevation, time: Any joint swelling from trauma needs to be attended to for rapid recovery, including ice, immobilization or support, and elevation above heart level. Time is always the great healer. Your injury will heal faster, if you take care to do these things initially. Will not work as well after a week out from your injury. Good that you didn't break any bones, or injured your knee any worse.

Time: It is likely just a contusion or sprain and will resolve with time especially if the MRI did not show any other significant findings.