Story
After the board is populated yopu can grab the bootloader and follow the Feather M0 instructions found here: https://learn.adafruit.com/proper-step-debugging-atsamd21-arduino-zero-m0/restoring-bootloader
More details and code: https://github.com/mike-rankin/SAMD21G18A_Test_Board. This project is reposted with the approval of this project creator. He is a good DIY maker who designs custom ESP32 IoT projects using Altium Designer, Arduino IDE and Fusion360. Welcome everyone to follow him. This is his GitHub account, Mike Rankin, where you will explore more excellent projects.