An Examiner holds an Authorisation; most are issued Nationally and are usually only valid in a State covered by the issuing administration. I gather that under EASA if you hold an Examiner Authority in one EU State it will be valid in all EU States.
To use an Examiner Authority in an unconnected State you would need to get an Authorisation issued by the Aviation Administration in that State. They may do this on the basis of your existing Authority. It depends how much they need an examiner.