Arduino Micro as ISP (flashing the bootloader of an Arduino Leonardo) – and thus goes by another day
Arduino Basics To Developing Bootloader For Arduino | Arduino
Arduino Install Bootloader on UNO, MEGA, NANO - YouTube
Arduino Projects
Pro Micro ATMEGA32U4 5V/16Mhz Module Met De Bootloader Voor Arduino Mini Usb/Micro Usb Met 2 Rij Pin Header Voor Arduino|micro atmega32u4|pro micromicro pro - AliExpress
Reinstall bootloader for an Arduino Pro Micro?
Arduino as ISP to Burn Bootloader on AVR Microcontroller - YouTube