You create a parameter named Choose Region fiat contains values from a field named Region.

https://kb.tableau.com/articles/howto/filtering-data-with-a-parameter?lang=fr-fr

After creating a parameter named Choose Region, you want to use it to filter the chart based on the user ' s selection. To do this, you would create a calculated field with the formula [Region] = [Choose Region] and add this calculated field to the Filters card. This will dynamically filter the chart to display data only for the region that matches the user’s selection in the Choose Region parameter.