Hello
I initially followed the steps from Freerouting launcher which is supposed to simplify the use of Freerouting (ie fill in the correct paths) but this required adapting to work in the Mac environment.
The updated script is at https://github.com/fabrataz/KiCadFreerouteScript - with explanations.
This has been tested and currently running in KiCad v5.1.0.0 (under Mojave)
Fabrice