Hi, my galaxy S23 ultra is Vietnam variant(XXV). Recently I moved to Canada and got a SIM that has 5G in my area. But unfortunately the 5G bands are locked in my device and I can not unlock it. I did some research online and found some tools to unlock but nothing helped. Is there any official way to unlock those 5G bands?
You need to find out what bands your carrier supports and if those bands what's available on your area. Then you need to find out what bands your phone supports. If you get a match you should need able to get coverage if your provider doesn't do something like not allow your specific device to do so (you can find that out by calling them).
For example, if you're on Rogers and your area only had band 71 support from them, and your phone doesn't support band 71 (likely if it's an international phone), you won't get a 5G connection.
Were you trying to enable bands via the service menu?
He bought a Sim so he joined a network. The rep has to add 5G to his account in order for it to be connect able. The 5G has to be enabled on the phone, in settings. If it doesn't work at the store it won't work any where else.
