Here is the code and the worksheet.
Some things to know:
There is a new sheet called List, this will be the sheet with the data source for the drop down. This sheet can be hidden or very hidden. If you want very hidden then in the project explorer from the view menu choose properties and left click to select the sheet and in the properties window next to Visible choose very hidden.
The macro code can be moved to the activate event for the sheet with the drop down so that it will run every time that sheet is activated or you can leave it where it is and just run it as needed. There is a dynamic named range on the list sheet which is referenced in the drop down as the source for data.