Unlocking country lock on iPhone

Unlock what? There are a number of different types of lock on the iPhone. If you are referring to changing carriers, if the carrier you had before had a lock on your device, you need to contact them. See the information in this support document. How to unlock your iPhone for use with a different carrier - Apple Support

There is no such thing as a ‘country lock’.

If it is carrier locked, only the carrier it is locked to can unlock it.

How is it “locked” ???

Nothing in your OP provides any indication.