New fields added to source tables feeding a Tableau extract will automatically show in the extract after its next data refresh.
On the other hand, if a source field was available during the extract creation but was set to hidden and not used in formulas, Tableau will NOT bring in its data automatically.
If fields are missing from a Tableau extract from Tableau Server:
On Tableau Desktop → Data → New Data Source → Tableau Server → select the desired data source → Connect.
Right-click the data source → Create Local Copy → save it locally.
Right-click the locally saved data source in Desktop → Extract → Remove → Remove the extract and delete the extract file → Ok.
Now you should have access to all fields feeding into this data source. Use the Search box on the left panel to find your fields. If you don’t find some, click the Arrow Down by the Search box → Show Hidden Fields. Search again.
After you make field changes, you need to re-publish the extract: right-click on the locally saved data source → Extract Data → Extract → Save it. Your Tableau Desktop needs direct access to your data warehouse to perform this task. It might take some time to load the extract data.
Once the prior step completes, to overwrite the prior version from the Tableau Server: right-click again the data source (now it’s an extract) on Tableau Desktop → Publish to Server → be sure to select the correct Project and data source name, it should show “Data source name is already in use.” → Publish.