The holder of a JAR-66 licence may get a Part-66 licence by conversion only when the licence has been issued by a JAA Member State which has successfully completed the JAR-66 Review Board process. If a country is not in the list shown in this EASA document, no conversion can be made.
More details are shown on the Mutual recognition page
The holders of a JAR-66 licence issued from a country not in this list are not eligible to a conversion. They are required to demonstrate compliance with all requirements.