Find non repeated characters in a string

Good time of day, Maria!

Please check the attachment. User Defined Function used, macro must be allowed.

Function Rio_Join$(StrA$, StrB$)
    Dim i&, j&, k&, StrC$
    Rio_Join = StrA
    For j = 1 To Len(StrB)
        k = 0
        For i = 1 To Len(Rio_Join)
            StrC = Mid(StrB, j, 1)
            If Mid(Rio_Join, i, 1) = StrC Then
                k = 1
                Exit For
            End If
        Next i
        If k = 0 Then Rio_Join = Rio_Join & StrC
    Next j
End Function