The pen holder part consists of two parts, the base that'll be connected to the printer tool head and a griper part that'll act as a clamp for the pen.
I believe that the hardest part of this design was finding a way to connect the pen holder to the tool head, but fortunately, I found these four M3 spacers that connect my extruder to the stepper motor. I four more 50mm M3 spacers to connect the pen holder base, and four 15mm M3 screw to connect the clamp.
This part is used to make a 6mm offset in the Z-axis to avoid hitting the nozzle to the bed.
Software (CURA profile)
Adding a new material
You need to change your CURA settings to be able to use your printer as a 2D plotter. for that, I suggest adding new material so you'll be able to access the settings anytime.
With a 2D plotter like this, you can only use bitmap pictures that consist of only 100% black and 100% white, because a pen can't make shades, well actually it can but in this application, it can't.
For making shadows you can try using different textures for different darknesses, search for "bitmap art" and you see what I mean.
Well tbh, I don't know what else I can say about this upgrade, It's a really simple thing, but If you need any more information about it, just ask me in the discussion, I'll answer.