Hi Basil,
That error means your Surface Go is still trying to use the update files from the flash drive. Since the update failed, you’ll need to fix Windows manually or reinstall if needed.
Download the correct ISO for your device from the Surface Recovery Image Download - Microsoft Support . You'll need your serial number.
On another PC, download the recovery image for Surface Go from the link above. Format a 16GB or 32GB flash drive to FAT32. Use the Create a recovery drive tool (search in the Start menu) and uncheck “Back up system files.” Copy the recovery image files to the flash drive.
Plug the USB into your Surface Go. Hold Volume Up, then press and release Power to get to the UEFI menu. Set the USB drive as the top boot priority, then exit and restart. Select “Recover from a drive” and then “Just remove my files.”
Where did you get the ISO you used before? What exact model of Surface Go do you have?
Let me know if you run into any issues.
Cheers