I did a very similar process as the video, except I used the normal power supply for the printer with the Arduino and RAMPS connected but the steppers disconnected. It’s pretty easy to connect one side of your multimeter to the board ground with a clip. Hold the positive probe to the via they show in the video and turn the pot to set your voltage at 0.7V. If you follow the instructions in the video all the way you’ll squeeze the last bit of power out of your stepper, at the cost of a lot of heat you’ll have to dissipate. At 0.7V you won’t have to worry about heat and you’ll still have plenty of power to move around much faster than you really need.