In the present numerical study, we investigate the oscillatory control on a two-dimensional bi-stable jet discharged from a flip-flop nozzle. Oscillating jet can be used to flow control actuators but the oscillatory frequency of the nozzle has a significant dependence on the geometric configurations of the nozzle such as the length and volume of the feedback tube and the entrance pressure. On utilizing this jet as flow control actuators, it would be desirable to be capable of switching the oscillatory frequency of the jet without modifying the nozzle configuration. We conducted DNS of the oscillating jet at Re=100. At first, the pressure difference across the deflected jet and the oscillatory frequency f_0 which is proper to a given nozzle configuration were investigated using the periodic boundary condition on the control ports of the nozzle. Then we computed the jet using pressure boundary conditions instead of the periodic one. Depending on the input pressure ratio, when the ratio of the input pressure frequency f_<in> into f_0 was less than unity (f_<in>f_0=0.48), it was found that the oscillatory frequency of the jet could be rocked in f_<in>.