How to use trigger code for a single update statement?

Gurus,

I need to take some code I wrote in a trigger and update existing data.

Trigger:

create or replace
TRIGGER exchange_experts_question BEFORE
  INSERT OR
  UPDATE ON PRS FOR EACH ROW

Begin

If
:new.prsvf14c in ('1','00','0',null) and to_char(:new.prsprsc/100,'999.99') like '%.00'
    Then
      :NEW.PRSVF19C := '$'||FLOOR(TO_CHAR(:NEW.PRSPRSC/100,'fm999.00'));
END IF;
END;

How would I take this code and update the existing data with this criteria?

Procedure?

Any help would be great.