remplace text

Hi every body.
I have a text.... many lines, end of line is OD OA
I want to change the beginig of each line
the first 5 bytes remplaced by   "¿"

Below my code... sorry it is not OK
Who have an idea ?

I use DOS  Operating System    compiler is A86

mov   si,0080h
lodsb
cbw                   ;extend AL to AX
xchg  bx,ax           ;swap size to bx for indexing
mov   byte [bx+si],0  ;null terminate command line
mov   di,inbuff       ;our buffer
; dospc: cmp   byte [si],32   ;any leading spaces ? ; jne nospc ;nooo
inc   si              ;yeahh, dump it ; jmp  dospc ;check next
nospc: mov   cx,1                   ;we're here, so we got one arg
copy1: lodsb                        ;load byte SI to AL
cmp   al,0                  ;0 ?(end of line)
je   done                   ;yeahh
stosb                     ;noo, move AL to DI, incrase DI
jmp short  copy1            ;go on
done:  mov   byte [di],0    ;null terminate END of PARSE
gotfile:
mov   ax,3d12h              ; open file  READ/WRITE/NO SHARE
mov   dx,offset inbuff      ;filename
int   21h

fopok: xchg ax,bx
; ; handle ; mov word [bytes],256 ; buffer size
; ; NOTE BX will not change  I put value 0 into count 1 and 2
; ; xor ax,ax ; mov offset count1,ax ; clear out ; mov offset count2,ax

readlop:    mov   ah,3fh          ; read file ;  mov bx,[filehandle]
mov   cx,[bytes]          ;read buffer full
mov   dx,offset address   ;buffer
int   21h
cmp   ax,0              ;nothing read ? (end of file)
ja   main               ;nooo, do the work
jmp short  quit         ;yeahh, we're done
main:
mov   [bytes],ax        ;bytes read
mov   cx,ax             ;counter
mov   si,address        ;file buffer

push cx
mov cx,5               ; i want to remplace 5 bytes by ¨
push bx                ; save the handle
xor bx,bx              ; will be used like counter

mloop:
lodsw
inc bx                 ; count
inc bx
cmp ax,0D0Ah            ; is it end of line ?
jz mloop
lodsb
inc bx
cmp al,0Dh
jz mon0a
mov byte si,0A8h         ; new line, then remplace by ¨
lodsb
inc bx
mon0a:
cmp al,0Ah
jz mloop
mov byte si, 0A8h          ; again change with ¨
loop mloop
pop cx
sub cx,bx                  ; resize  file buffer
pop bx                     ; restore handle

mov ax,4200h                     ; s set file position beginning
mov   cx,[count1]        ;most significant part of offset
mov   dx,[offset count2] ;least significant part of offset
int   21h

mov  cx,[bytes]          ;get offset size
mov  dx,[offset count1]  ;the most significant part
mov  ax,[count2]         ;the least significant part
add  ax,cx               ;add offset to least sig part
adc  dx,0                ;add with carry
mov  [offset count1],dx  ;save them back for next loop
mov  [count2],ax

mov   ah,40h              ;  write to file  mov bx,[filehandle]
mov   dx,offset address   ;buffer
int   21h
cmp   word [bytes],256    ;less than 256 bytes left ?
jb   quit                 ;yeahh, must be last read
jmp short  readlop        ;noo, go on reading
quit:                    ; cmp word [filehandle],0 ;any filehandle

mov   ah,3eh             ; close file
int   21h
nofile: ret                      ; int   20h

; DATA
bytes        dw   ,100h ; size buffer for file
filesize:    db:   0,0
filehandle   dw    0,0
count1       dw    0,0  ; at the begining, value must be 0
count2       dw    0,0
inbuff:      db:   0,0
address:     db:  ,0,0