If a field used in Tableau is removed or renamed in the dataset, there will be an exclamation point next to it when you refresh the Data Source. If the column is removed, you can't do anything except put it back. More often, the column is just renamed and, in Tableau, you can replace the references to the old column with the new one.

Let me illustrate the process with the Sample-Superstore dataset. Let's say that the Region column was renamed New Region:

1. In a Workbook, I display the Region in Rows:

2. I refresh the Data Source—the Region pill turns red, and in the Data pane, there is an exclamation mark next to the Region field:

3. To correct the error, I right-click on the Region field and select Replace References...:

4. Select the new field that replaces the old one. In this example, it's New Region.
5. The old field, Region, is removed from the Data Source and, in the Worksheets, the pill is now using New Region. You can see the result in the following screenshot:

Easy, isn't it? Now that you have a clear view of how to use and refresh your Data Source, it's time to see how to customize it.