I had a lot of questions on what a 3D printing pen can be used for.
Here I did a quick ugly hack \ repair on my wife’s shaver. The power supply broke as in the pictures below.

I did a quick repair to demonstrate the usefulness of a 3D pen.

This is the 3D printing pen that I have and that I used for this repair.

I used the last piece of white PLA of a discarded roll to do the repair.

I filled the hole up with the pen from 1 side making sure that i melted the PLA into the power supply plastic to ensure a good bond between the 2 materials.

After that I used a fine file to give it  some shape to fit into the multiplug.
I did not spend a lot of time on this to make it look beautiful.
I was more interested in function, meaning a working power supply.

I have used my 3D printing pen for a variety of projects from joining 2 printed parts to 3d sculptures.

I hope this gives you some ideas of what else to do with your 3D pens.