Next And Previous Navigation Buttons?

I would like to have a "PREVIOUS" navigation button in a workbook that goes back to the previously activated worksheet, which may or may not be physically the previous worksheet in the workbook. In other words, if I go from Sheet #1, to Sheet #3, to Sheet #5, I'd like to return to Sheet #3 from Sheet #5 (rather then navigating back to Sheet #4).

"Open VB editor and double click 'Thisworkbook' and paste this code in on the right:

Private Sub Workbook_SheetDeactivate(ByVal Sh As Object)
lastsheet = Sh.Name
End Sub

Then right click 'ThisWorkbook' and insert module and paste this code in

Public lastsheet As String
Sub Select_Last()
Sheets(lastsheet).Select
End Sub

Whenever a user changes sheets, the name of the last sheet is now held in the variable 'Lastsheet' so if you assign a shortcut or button to the code then the last used sheet will be selected."

My problem is that when I want to assign the macro, I can't find macro name that looks anything like the above in the drop down list of Macro Names. how to assign the macro to a button?