Connect GRBL controller board usinf USB

I am a bit stuck.
I want to control a GRBL controller board (based on Arduino Mini) with a WiFi-Kit-32 in order to send GRBL Data to the WiFi-32-Kit using WiFi, and then the WiFi-Kit-32 copies the data to the controller using USB. The WiFi-Kit-32 acts as a WiFi to USB gateway. I was able to do that with a Raspberry Pi and Python, but so far completely stuck with the WiFi-Kit-32.
How could I do this? Are there any examples on how to use the USBPort?
Any inputs mot welcome.
Best regards
Thomas