A DC offset can be added to a pure AC signal by using a clamping circuit. The AC signal is passed through a capacitor and the clamping voltage is applied though a PN junction diode. The connection diagram and the screenshots for both the PC and phone versions are shown below. Clamping a 3 volts AC signal using 1 volt DC lifts the lowest point (-3V) to ~0.3 volts, that is 1 volt minus the drop across the diode.
Reverse the diode direction a apply negative voltages to clamp in the reverse direction.