First of all, lets flash Adafruit’s NRF52 bootloader for easier future flashing
My J-Link was “Broken. No longer used” - or so the JLink tools said (AKA bought from e-bay). So I had to go to openocd).
Connect the J-Link (or any SWD capable debugger supported by openocd - even an FT232 breakout will do) to the target - I have a Bluefruit by Adafruit.
git clone https://github.com/adafruit/Adafruit_nRF52_Bootloader cd Adafruit_nRF52_Bootloader make BOARD=feather_nrf52832 all FIRMWARE=lib/softdevice/s132_nrf52_6.