[Koha] Remove 952$x from search index

[Polonec Viliam, Ing.]

I need to disable searching in  non public note field in OPAC.
I check settings in  /etc/koha/zebradb/marc_defs/marc21/biblios/biblio-koha-indexdefs.xml
but there is no 952$x setting.
How can I disable searching in 952$x


thanks


Viliam