Press the BOOTSEL button and hold it while you connect the other end of the micro USB cable to your computer:
Short the rst pin to ground twice in quick succession, and the tool will detect the pro micro in bootloader mode
Note that when this is done, you only get around 8 seconds to reprogram the guitar, so you will need to be quick and its best to open the config tool first.
Install Arduino IDE https://www.arduino.cc/en/software
From the file menu, load up the EEPROM clear example sketch, as shown below:
Note: It is important to hit upload first and then short twice, as the Arduino only stays in it's programmable mode for 8 seconds