Unfortunately, there isn’t a dedicated volume button or knob. While there is adjustable Gain and Threshold features, it is not the same controlling volume for hard of hearing or adjustable sound. While Gain and Threshold have their functions, you must rely on headphones with a volume control if you want to be able to adjust it.
The VCO (Voltage Control Oscillator) system is what determines audio volume based on the signal strength of the target. So, both the pitch and volume will increase the stronger the signal. This could mean it’s close to the surface or large in size. Weaker signals may be low in tone, small in size, and may be buried deeper.