You cannot change the definition of a datasource from a button on the dashboard. You can only change the connection from within Tableau by using the connection editor itself.
Perhaps tell us a little more about what you're trying to achieve?
Thanks for the Response!
I have two tables from the source (Mysql) , have loaded into tableau using mysql connector.
Now i want to make join (left , right or Full) of these tables from the dashboard by a click, not at the Data Source Tab.
Please find the attachment
Like I said, you cannot edit the connection outside of the Data Source tab within Tableau.
Why do you want to edit it from the dashboard? What's the purpose?