Try a Case select method
Function Convert(ByVal Value As String) As Integer
    Select Case Value
        Case "A"
            Convert = 10
        Case "B"
            Convert = 11
        Case "C"
            Convert = 12
        Case "D"
            Convert = 13
        Case "E"
            Convert = 14
        Case "F"
            Convert = 15
        Case Else
              ' Assuming Value should be converted to an integer if it's not A-F
              ' You might want to add error handling here if Value isn't always a valid number
              If IsNumeric(Value) Then
                  Convert = CInt(Value)
              Else
                   ' Handle the case where Value is not A-F and not a number
                   ' For example:                
                   Convert = 0 
                   ' Or raise an error, or return a specific error code
              End If
        End Select
End Function