@Husni2020Be nice and be polite otherwise people will NOT help you.
If you want to use the AT!ENTERCND command please ask netgear on their forums for help as Optus will NOT be able to help you and I have not seen this command aground the various wed sites support areas in OZ for use with the AC800s.
You have been given the answer that that works for other AC800s end users in OZ that allows you to lock/unlock bands. Remember you can google yourself if you do not like the command to find another command to use or want help from somewhere else.
BTW if you had googled and looked up how the AC800S works then you would have found that the AC800S web interface only shows one band and when CA kicks in will still only show one band and from what I understand CA will only kick in after a while when downloading and will most of the time be off.