If the "Service 02" error appears, please connect the band with the app and accept the firmware update.
In case this doesn't help and the error is still there, please try the following steps.
1. Turn on the device - wait for the Service 02 error - turn off the device
2. Turn on the device - wait for the Service 02 error - turn off the device
3. Turn on the device - wait for the Service 02 error - turn off the device
After you do the recommended actions three times as specified above, please try to update the firmware once again.
If this doesn't help, as a final step, please leave the device for 3-4 days and let it discharge completely. After that, put it on charge again and see if the error has disappeared.