Debug Settings for J-Link Target

I’m trying to use an external debugger (J-Link Base) instead of CMSIS-DAP on my nRF52840-DK. I’ve got the J-link device added as a target, but I always get a timeout when waiting for the gdb server to start. This hasn’t been a problem when debugging through CMSIS-DAP, so I’m assuming it’s to do with the configuration for the J-Link target.

a) Where are the configuration files stored? I’m on mac OS, but I presume the directory trees are similar.

b) How can I modify the target/project to generate my own settings?