[Koha] Country subfield in framework

I'm editing subtags in a MARC21 framework, and trying to use 044.c for book's publication country. At Tag subfield structure -> Edit -> Other options; I set authorized value "COUNTRY" and thesaurus "GEOGR_NAME" Then, when using this framework on cataloguing a book, this subfield appears with a dropdown box with "No matches found". How can I prepare values to this box be linked to? Thanks.