The right way to take a walking step is to strike with the heel in front but the rest of the forward foot slightly off the ground, then rolling through the step from heel to toe. By the time the toe is on the ground, you are midway into the next step and the forward foot is now the rear foot and ready for the toe to give you a good push off into your next step.
This heel strike-roll through-push off with the toe is only possible if your shoes are flexible. If you are wearing stiff "walking" shoes that are really only good for standing, you may not be able to roll through a step from heel to toe. Instead, the stiff shoe forces your foot to slap down. Your body may have given up on even trying and your walking stride is more like a flat-footed stomping march.
To correct it, take a couple of minutes during a walking session to think about what your feet are doing. Are you striking with the heel and rolling through the step? Is your rear foot giving you a push off?
There are two things to think about to change it. First, think that your forward foot is showing its sole to somebody facing you.
Second, concentrate on keeping the rear foot on the ground longer and really giving that push off.
If it is impossible to do this in your present shoes, it's time to buy better, flexible walking/running shoes. Walking Shoe Guide