Problem è Convert the upper case string to lower case

DATA_HERE SEGMENT

                STRING DB 'WELCOME TO I.B.M.F.T. $'

DATA_HERE ENDS

STAK    SEGMENT STACK

                DW 1000 DUP(0)

STAK    ENDS

CODE SEGMENT

        ASSUME CS:CODE, DS:DATA_HERE, SS:STAK

START:          MOV AX, DATA_HERE

                MOV DS, AX

                MOV AX, STAK

                MOV SS, AX

                MOV AH, 09H

                MOV DX, OFFSET STRING

                INT 21H

                MOV BX, OFFSET STRING

                MOV CX, 0FFH

NEXT1:          MOV AH, [BX]

                CMP AH, 41H

                JB NEXT2

                CMP AH, 5BH

                JA NEXT2

                OR AH, 20H

                MOV [BX], AH

NEXT2:          INC BX

                LOOP NEXT1

                MOV AH, 09H

                MOV DX, OFFSET STRING

                INT 21H

                MOV AH, 4CH

                INT 21H

CODE              ENDS

                END START