Late but better than nothing I guess.
Sub Convert2DTo1D()
Dim arr2D(1 To 2, 1 To 3) As Variant
Dim arr1D() As Variant
Dim i As Long, j As Long, k As Long
' Populate the 2D array
arr2D(1, 1) = 1
arr2D(1, 2) = 2
arr2D(1, 3) = 3
arr2D(2, 1) = 4
arr2D(2, 2) = 5
arr2D(2, 3) = 6
' Determine the size of the 1D array
ReDim arr1D(1 To UBound(arr2D, 1) * UBound(arr2D, 2))
' Populate the 1D
array k = 1
For i = 1 To UBound(arr2D, 1)
For j = 1 To UBound(arr2D, 2)
arr1D(k) = arr2D(i, j)
k = k + 1
Next j
Next i
' Print the 1D array to the Immediate Window
For i = 1 To UBound(arr1D)
Debug.Print arr1D(i)
Next i
End Sub