I've been rading through the documentation for the Muon carrier board (Muon datasheet | Reference | Particle), but I can´t find out which pin on the expansion connector can be pulled low to trigger a reset. Am I overseeing any spot on the documentation? Any guidance would be greatly appreciated.
You cannot reset the M-SoM from the 40-pin expansion connector.
The expansion card cannot reset the M-SoM mainly because the expansion connector is mapped to GPIO for compatibility with Raspberry Pi HATs and reset can't be used as GPIO.
Isn't there any additional connector on the carrier board to trigger an external reset? I’m quite surprised by this design choice.
I plan to enclose the carrier board in a plastic case, where it should be possible to reset the device using an external button. This design choice complicates that implementation, as there is no straightforward way to trigger a reset externally.
For your use case what I would do is use the 2x5 JTAG debug connector. You can make a small cable with the matching plug on one end, and on the other end wires that attach to your external switch that connects the /RESET and GND pins together when pressed.