Window application access local database and server database too but one source at a time

@Aravindba your idea seems good just one problem(I'm assuming the user rights you are asking about would be in the database) would you not already need to make the connection to the specific database in order to find that information or are you referring to windows authentications?

@Tilak Have you thought of maybe writing the database connection strings for each application into the registry of the computer that it is installed on? That way on each installation you would just need set the path to the database once and on each connection that you make in the application you refer back to the registry.
Just a thought

Also just to verify, the clients you refer to are in different "companies" or is it just different terminals that will be using the application?

Why I ask this is because if they are different "companies" will they always have access to the server database or will the database be hosted on their own servers?
If it is on their own servers then you will have to change your connection string for each deployment of a new "company" (then writing the connection to the registry might be the best practice(instead of publishing new versions for each client) for something like this you would want to keep your solution as generic as possible especially when it comes to updates for the application)

A personal note, It might not be the best practice to have the databases run on local machines(unless there is only one machine that will be using the application)

Use application config file to store many connection strings and use a mechanism to choose specific connectionstring for specific user. That should do it i suppose

There are many questions that come to mind. In the most generic sense you provide a connection string from App.config or other runtime configurable place, never hard code connection string.

Is the database going to be accessed by multiple clients, do the clients need to know about changes made by other clients? If the database is local for some clients, does it need to synchronize with the server database such as an offline client?