Exploiting prediction error identification methods, this paper proposes a measurement data-driven approach to monitor power system oscillations at a power plant, identify a data-based model using an input signal and redesign the plants power system stabilizer damping controller to mitigate the observed oscillations under ambient conditions and multiple operating points. The advantage of the proposed methodology is that the damping performance can be monitored continuously and the redesign only requires measurements at the power plant along with the controller's structure, which are known by the power plant operator.