An efficient locking technique based on optical feedback is demonstrated to suppress jitter on the rf beat note between the two modes of a dual-frequency $\mathrm{Yb}:\mathrm{Er}$ glass laser. The method consists of a self-injection process in which one selected mode serves as a master oscillator to lock and stabilize the second mode via a frequency-shifted optical feedback. The beat note adjusted near $170\mathrm{MHz}$ was stabilized with an accuracy of $250\mathrm{mHz}$ using an optical feedback loop with a double pass through an acousto-optic modulator. The beating note can be tuned over $300\mathrm{kHz}$ by controlling the reference oscillator. The extensions and limitations of the technique are discussed.