Thank you all for the reply. here is the solution,
these are service accounts created using windows authentication and to test the user works fine or not u need to follow below steps,
Connect via SSMS : right click the SSMS in the task bar then Ctrl + Shift + right click on the SSMS icon then you can see RUN AS DIFFERENT USER -> click on that then share the Service account credentials then it will connect as windows authentication.
Connect via Application using Connection String: set this parameter in the connection string then it will take service account credentials: Integrated Security = SSPI;