ATmegaa32U4 USB with internal RC clock Burn Bootloader

[Harmony]

Does anyone know how to Burn Bootloader to ATmegaa32U4 with internal RC clock?
When I plug my custom Atmega32u4 PCB connects to Windows, it shows 'Unknown USB Device'. I think it's because I didn't put the crystal on, but ATmega32U4-AU has default external XTAL.
So, I want to Burn Bootloader to ATmegaa32U4 with internal RC clock. I have read this post: https://www.eevblog.com/forum/microcontrollers/atmegaa32u4-usb-with-internal-rc-clock/
But I dont know how to use the "Caterina.hex" and "makefile". I have searched some relative information online, but still couldn't figure out.
Please help

I am using an Arduino Uno as a programmer via the ISP interface.
My computer is Windows 10.