I have got my new EleksDraw assembled. The pen holder is way too low if I want to draw on paper on the same platform. So I put a 10mm x 10 mm x 25mm wood block in it with 3M tap. And then the pen holder works fine.
It is kinda tricky to assemble the servo and the pen holder. It required playing with the laser on/off button a lot to figure out the right angle.
Another trick is that one of the holder brass pipes should not be fastened too tight. It got to be loosed a little bit. Since there are two brass pipes holding two bars. If both two pipes are fastened very tightly, it would be too hard for the servo to lift the pen, and also too hard for the pen to fall down by its weight.