Hi Saikat Gope, assuming that your plant a damped oscillator (which I attempted to create from your output response), if the plant is undisturbed, then set the reference input xref equal to 0 should do the trick. If the plant is operating in the presence of a constant disturbance, then design a controller with integral action such as the PID control. The integral action can be employed to reduce the steady-state error to zero.