Use single Reporting service Report to access multiple database from asp.net

Hi,
I have a report in Report server.
There are three client application accessing the same report and using report viewer control for display purpose.
Now all three application shows same data. I need to modify my asp.net (C#) code or report to work based on the calling application and display of their own.
Please advice me how to proceed further.
If you are not clear on my description please let me know.
PS: All three application DB structure are same, used by different clients.
Thanks

Each report needs to retrive data from different database. (But all Database structure are same, so the same stored procedure is available in all DB's)

SAy for example:
Appln A , Appln B & Appln C - all are calling the same RS report with same parameters.

When ApplnA calls the report then our RS report need to connect to Appln A's DB (i.e. DB A) and retrive data.

Currently All three applications are getting DB A's data, not their own data.

How to achive this ?