Use the Duplicate command to copy a column. If you want to make significant changes to a column, it’s a good idea to duplicate or copy the original column, and make your changes to the new column, so you don’t inadvertently cause refresh errors down the road. For more information, see Handling data source errors.
To open a query, locate one previously loaded from the Power Query Editor, select a cell in the data, and then select Query > Edit. For more information see Create, load, or edit a query in Excel.
Select the column for which you want to make a copy.
Select Add Column > Duplicate Column.
You probably want to rename the new column. For more information, see Rename a column.