In this work, the oscillatory control of a two-dimensional bi-stable jet discharged from a flip-flop nozzle is investigated. The flip-flop nozzle, which has several engineering applications, is known as a fluidic device that can produce an oscillating jet without any moving parts. Its oscillatory frequency strongly depends on the nozzle configuration. The aim of this work is to estimate the external force required to oscillate the jet at an arbitrary frequency using vibrating diaphragms on both control ports of the nozzle. A relationship between the operating amplitude and frequency of the diaphragms was derived from an approximated momentum equation. In order to verify this relation, numerical simulations of the oscillating jet were conducted at Re = 100. It was found that the jet oscillation can be synchronized with the diaphragm's vibration when the operating velocity of diaphragm satisfies the proposed relation.