It increase HR during exercise but heart muscle get strongers so that you can reduce your nonexercise
heart reate by 10-20 beats. because most of hours
people do not exericse, so overall heart beat
dropped. It is a matter of simple arithmetics.

Say now you nonexercising HR is 70 bpm and you do not exercise. If you start exercise, your nonexercising HR
will be reduced to 60. Your exercising HR will be
130 bpm and your exercise 1 hour a day

So the net reductiuon of HR per day is
10*24*60-60*60=180*60=10800 beats.

And one year, your save 3 million beats by doing exercise,