How do you tune a suspension air shock on a bike for light riders like me?

Looking at the specs it does not appear to have an adjustable air shock. Bikes at this price point typically use either a coil spring or a gas strut (similar to the type that holds the hatchback open on a car). The dampening rate is set by the manufacturers design. In some cases larger frame sizes will be stiffer than smaller sizes. The reason being that if you are taller you typically weigh more and need a stiffer suspension. This also means that if you are tall and thinner than average the suspension will be too stiff. Some forks will have a plastic knob that when turned counter-clockwise will give a slightly softer ride. You can try to soften the ride by lowering the pressure in the tires. This can only do so much before you start getting flats from pinching the tubes.