@adventureman See the guides on the wiki, on the left side. Work through them to understand how to change the configuration with config.g. Specifically for changing the motor direction, see https://docs.duet3d.com/en/How_to_guides/Commissioning#h-10-check-stepper-motors and see the sub section 'Reversing a stepper motor". But really you want to start at the beginning of this page, and check through everything.
Ian