Tableau is a reporting tool--so therefore, any data that needs to be updated needs to be done on the data source itself. A calculated field could possibly be created to fix something on the front end, but it won't change the data.
Hope this helps!
Is there is any way that we can achive this functionality , by using socme scriptitng like R OR PHP?
I saw one post which says we can update database from tableaufront end, below is the URL for your reference.