How to merge two 16 bit dW in one DD number in 8086 assembly

Question

with the following code I calculate first 30 elements of fibonacci sequence. Note that every two element of arr represent one element of the fibonacci sequence while the fibonnaci numbers after 26th element will need more than 2 byte to represent.

StSeg   Segment STACK 'Stack'
        DB 100H DUP (?)
StSeg   Ends

DtSeg   Segment
        arr   dw 62 dup (?)
        the30 dd ?
DtSeg   Ends

CDSeg   Segment
        ASSUME CS:CDSeg, DS:DtSeg, SS:StSeg
Start:
        MOV AX, DtSeg ; set DS to point to the data segment
        MOV DS,AX
        
        ; PROBLEM: STORE FIRST TWENTY ELEMENTS OF FIBONACCI IN AN ARRAY FROM MEMORY.
        ; SOLUTION:
        mov bx, offset arr
        add bx, 2
        mov [bx], 00H
        add bx, 4
        mov [bx], 01H
        ; inited fibo[0] = 00000000H and fibo[1] = 00000001H    
        mov cx, 29; make while loop counts 29 times.
        while:   
        
        ;first part addition
        mov ax, [bx]
        mov dx, [bx-4] 
        add ax, dx
        mov dx, 00H
        jnc else
        mov dx, 01H          
        
        ; second part addition
        else:
        mov [bx+4], ax
        mov ax, [bx-2]
        add dx, [bx-6]
        add ax, dx
        mov [bx+2], ax
        add bx, 4
        loop while
        
        
        MOV AH, 4CH
        MOV AL, 0
        INT 21H
CDSeg   ENDS
END Start

my college assignment asks to store the 30th element in variable named the30 which DD but I do not know how is that even possible when all of the registers are 16 bits at most.

Is there any way to do that?