There's a couple of types of locks on a Samsung Phone.
The first is the Region Lock you mention.
To remove that a culmitive call of 10 minutes needs to be made in the country of origin using a local sim card and the call is made to a local number.
Another option is to contact the Samsung Support Department for that country and ask them to remotely remove the Region Lock.
The 2nd is some phones are locked to a particular network if the phone was supplied by a mobile network as part of a mobile phone contract.
The unlock to all networks usually is carried out by the network that it's locked to.
They will have their own set process and a criteria to meet before unlocking.
If Samsung supplied the phone directly then it should already be unlocked to all network's.
Current Phone ~
Samsung Note 20 Ultra 5G SM-N9860_256Gb SnapDragon 865+
Samsung One Ui 2.5/ Android 10.