You can use the console to read-out your current grbl settings as well as set new values. The key is that the setting in LightBurn match that of your firmware.
As for origin, change the origin in the device settings. If the image is mirrored left to right, swap the origin from left to right. If it’s upside-down, swap the origin back to front. Step 6, here:
https://github.com/…/Docume…/blob/master/DeviceWizard.md
Here is a helpful video covering Machine and Job Origin.