If you backed up the EEPROM and Flash, then restore those.
Then use the official firmware loader to put the official firmware back on the radio
If you didn't backup the EEPROM and Flash and you loaded voice prompts, then you can get away without restoring your backups.
But you will need to use the official CPS to upload a official codeplug, even a blank / default one, as the OpenGD77 codeplug is 80 channels per zone and the official codeplug is only 16 channels