That will do nothing for you.
The "Diagnostics" he is referring to is ECU codes, and if you didn't have any of those before the "ECU learning", you won't have any after.
If you had, say a bad oxygen sensor, it could cause the long term fuel trim to adjust. After that got fixed, then you could disconnect the battery and it would help because it takes so long for the long term fuel trim to adjust itself.
If the same oxygen sensor was going bad, you didn't fix it, and disconnected the battery, then it would run worse because there was no compensation from the trim.
The ECU is always adjusting itself because of input from the sensors. "Cleaning it" isn't something that you would need to do.