How can a criminal victim applying for immigration status request a certified supplement I-918B document?

criminal question for crime victims: hello I was crime victim in 1994 agravate assault I have te report for lesa. law enforcement supporth agency the I was crime victim bud I don,t go to the courth to testify agains to the person who assault me because I was treading .if I go the courth they going to reportme with inmigration.the judge don,t put charges to this person .and now I am apliying for visa U for crime victims bud may lawyer in miami told me the prosecutor needs to certify the supplement I-918B for crime victims. what I can do ?to the prosecutor sign may form? or can I reopen the case again? thank you