How to disassemble circuit board pen to replace refill
Take apart pen on a table or surface that you wont lose any parts.
Holding the pen body and the nib section, pull the circuit board section from the transmission assembly. It is a friction fit and may take some effort to pull it apart. Don't worry you wont damage anything pulling it apart.
Once apart unscrew the transmission body by turning it counterclockwise.
Be careful to not lose spring once you pull the refill out. Replace with new refill and reassemble. Do not use pliers to tighten transmission, hand tight only.