Need to re-write a MSSQL update statement to work in Oracle

UPDATE b1perm b1
   SET b1_app_status      =
      (SELECT r3.application_status
       FROM conv_app_status_update a, statyp r3
       WHERE a.spc = r3.serv_code
       AND   a.task_des = r3.r3_act_type_des
       AND   a.task_status = r3.r3_act_stat_des
       AND   a.process_code = r3.r3_process_code
       AND   r3.application_status IS NOT NULL
       AND   a.spc = b1.serv_code
       AND   a.id1 = b1.id1
       AND   a.id2 = b1.id2
       AND   a.id3 = b1.id3 )
 WHERE EXISTS
        (SELECT '?'
         FROM conv_app_status_update a, statyp r3
         WHERE a.spc = r3.serv_code
         AND   a.task_des = r3.r3_act_type_des
         AND   a.task_status = r3.r3_act_stat_des
         AND   a.process_code = r3.r3_process_code
         AND   r3.application_status IS NOT NULL
         AND   a.spc = b1.serv_code
         AND   a.id1 = b1.id1
         AND   a.id2 = b1.id2
         AND   a.id3 = b1.id3);