To enable I2C0 we need to edit
/boot/uboot/uEnv.txt to include the
GB-I2C0.dtbo overlay. This will enable the SDA and SCL labeled pins. Your uEnv.txt should look something like the example image below. Once added, save and exit the editor, and reboot your Giant Board. Once rebooted you should see the new interface in /dev/i2c0. You can now use it via CircuitPython.
Make sure to uncomment the line
enable_uboot_overlays=1 this allows overlays to load on boot:
# enable u-boot overlays enable_uboot_overlays=1