Biofeedback makes information about a physiological signal available to the person learning to influence it. The signal may involve muscle activity, skin temperature, or patterns in heart rate.
Understanding HRV feedback NCCIH describes heart rate variability biofeedback as receiving heart rate information from a device and using breathing techniques to change the pattern.
A better starting conversation Ask a provider which signal is measured, how the session is structured, and what outcome they plan to monitor. Compare the evidence for the intended use, not just the appeal of the technology.