My average heart rate even at rest is as high as 90 to 100 bpm, what is the best way to reduce it to about 70?

Why?: Your heart is regulated by a system of fine neurohumoral mechanisms - why are you trying to defeat them? If your resting hr is 90-100, there's a reason for it. That said, generally the better shape you're in, the slower your resting hr so working out and being keeping body mass index 18-25 will usually do the trick. Fever, anemia, anxiety, stress, exercise, xs thyroid etc. Increases it.