You need to change the values of a dimension without creating a new field.

You can create aliases for the members of a dimension by right-clicking the dimension in the Data pane or in the view and selecting Aliases. This changes how the values are displayed in the view, but not the underlying data. For example, you can create an alias for “Central” as “Midwest”.

In Tableau, aliases can be used to change the way dimension members appear without altering the underlying data. This is useful for display purposes and does not create a new field within the dataset.