Coulnd't use 5G network on iphone 12 Pro in Uzbekistan

If your carrier is not in that list, then they are not an official iPhone supported carrier. In that case, you need to contact your carrier to have them see about becoming one. You are probably getting a carrier file from another carrier, which is why you are not seeing the 5G setting. Not much you can do about that until your carrier is approved.

If you cannot access the APN settings, there isn't anything you can do. Because they are not an approved carrier, those settings are not available for you. No one here has any contact information from Apple. We are users only.

Your only other option is to contact your carrier and have them give you the APN settings to set up your phone for 5G service with them. You may need to get a newer SIM to do this.

You should ask your carrier if you need a special SIM for 5G.