NOTE: MakerGear does not recommend printing to the MakerGear M3 directly over USB.This requires disabling octoprint and all wireless features. Instead we recommend that you use Octoprint and the M3's built in computer to make the most of your M3. You can learn more about using Simplify3D with Octoprint here.
In order to connect your M3 to your computer via USB, you first need to shut down the M3s built in computer (the Raspberry Pi).
On the front of the printer there is a pushbutton. Use an Allen key or other small object to push the button and hold it down for 10 seconds. When you let go, you should hear 2 short tones followed by 4 more tones. This means the system has begun to shutdown.
It will take a minute for the system to shutdown. When the green light on the printer has turned off, the computer is shutdown.
For more information on shutting down your printer, see this article.
You can now connect your computer to your M3 via the USB port on the front of the machine, and use software on your computer to control your printer (like Simplify3D's machine control panel or Pronterface).
You're M3 computer will stay off until you have power cycled the printer by flipping the power switch off and on. Once the computer is on again (you can tell because the green light will be on) then you will need to shutdown the computer again to use the USB port.