how to drive high amp stepper motor 4 wire without driver
My question is how can I control the motor with a microController?


Simple answer - you can't.

First, output voltage. Yes, you can (within limits) adjust the output voltage. What are those limits? From the data sheet:


  Output Voltage Adjustment: +/- 10%


That is, by adjusting a small potentiometer on the supply, you can vary the output from 90% to 110% of the nominal 12 volts, or from 10.8 to 13.2 volts. This is nowhere near the 4.2 volts you're looking for.

Second, control inputs: there aren't any.

The way you use this is by applying power to turn it on, and removing power to turn it off. That's it.

Your observation that "it doesnt seem to have inputs to control via a microController" is spot on, but your hope that you can somehow use it as a controller anyways is what is causing you trouble.

TL;DR - You can't do it, and you need a controller as well as a power supply.