On each motor driver there is a voltage adjustment dial. NEVER turn the dial while power is connected or you will kill the driver.

In the bottom right corner is the GND pin.

A multimeter can measure the RMS current between these two pins. Ideally the RMS Current = Peak Current x 0.707. For a 0.3a stepper motor the RMS current would be 0.21

Measure the RMS current; turn off power; turn the dial 5-10 degrees. Repeat until the RMS current is correct.

Test your machine again to ensure smooth moving motors that do not get very hot. (they will still be warm to the touch.)