Ubuntu – Granting USB Root Access to Fender Mustang Plug

I'm a total Linux noob (learning little by little), and I am trying to get my Mustang Plug app to recognize my Mustang III amp that's connected via USB. I've found documentation that suggests the following:

"Various distributions allow only root to access USB devices of unknown type. To change this and allow users in "plugdev" group to also have access to Mustang amp create file /etc/udev/rules.d/50-mustang.rules (or /lib/udev/rules.d/50-mustang.rules on systemd systems) containing lines:

SUBSYSTEM=="usb", ENV{DEVTYPE}=="usb_device", ATTRS{idVendor}=="1ed8", ATTRS{idProduct}=="0004", GROUP="plugdev"
SUBSYSTEM=="usb", ENV{DEVTYPE}=="usb_device", ATTRS{idVendor}=="1ed8", ATTRS{idProduct}=="0005", GROUP="plugdev"
SUBSYSTEM=="usb", ENV{DEVTYPE}=="usb_device", ATTRS{idVendor}=="1ed8", ATTRS{idProduct}=="0006", GROUP="plugdev"
SUBSYSTEM=="usb", ENV{DEVTYPE}=="usb_device", ATTRS{idVendor}=="1ed8", ATTRS{idProduct}=="0007", GROUP="plugdev"
SUBSYSTEM=="usb", ENV{DEVTYPE}=="usb_device", ATTRS{idVendor}=="1ed8", ATTRS{idProduct}=="0010", GROUP="plugdev"
SUBSYSTEM=="usb", ENV{DEVTYPE}=="usb_device", ATTRS{idVendor}=="1ed8", ATTRS{idProduct}=="0011", GROUP="plugdev"
SUBSYSTEM=="usb", ENV{DEVTYPE}=="usb_device", ATTRS{idVendor}=="1ed8", ATTRS{idProduct}=="0012", GROUP="plugdev"
SUBSYSTEM=="usb", ENV{DEVTYPE}=="usb_device", ATTRS{idVendor}=="1ed8", ATTRS{idProduct}=="0013", GROUP="plugdev"
SUBSYSTEM=="usb", ENV{DEVTYPE}=="usb_device", ATTRS{idVendor}=="1ed8", ATTRS{idProduct}=="0014", GROUP="plugdev"
SUBSYSTEM=="usb", ENV{DEVTYPE}=="usb_device", ATTRS{idVendor}=="1ed8", ATTRS{idProduct}=="0015", GROUP="plugdev"
SUBSYSTEM=="usb", ENV{DEVTYPE}=="usb_device", ATTRS{idVendor}=="1ed8", ATTRS{idProduct}=="0016", GROUP="plugdev"
SUBSYSTEM=="usb", ENV{DEVTYPE}=="usb_device", ATTRS{idVendor}=="1ed8", ATTRS{idProduct}=="0017", GROUP="plugdev"

Verify that the "plugdev" group exists in your system, OR remember to use a valid group containing your user.

Now either restart computer or unplug amp and restart udev subsystem with the following command:

~ $ sudo service udev restart

or on systemd:

~ $ sudo systemctl restart udev"

I apologize if this sounds completely ignorant, but how do I create the file mentioned above?

Any help would be greatly appreciated. Thanks!