This module has a multi-turn trimpot (potentiometer) that you can use to adjust the LM2596’s output voltage. Since the trimpot has 25 turns of adjustment you can easily adjust the output of the module to exactly the voltage you need.
The simplest way to reduce the voltage of a DC supply voltage is to use a linear voltage regulator (LDO), but linear regulators step down voltage by dissipating the excess energy as heat and do not yield any current step up. Buck converters, on the other hand, can be remarkably efficient and provide a step up in current output. Buck converters are one of the best ways to provide a regulated voltage from a battery since they don’t waste near as much energy in the process of dropping the input voltage as a linear regulator would waste.