[Koha] subfield 9

The last days I'm trying to connect some authorities from Thesaurus Structure to some MARC21 fields using the 9 subfield but I'm facing some difficulties in the "hidden" section. In 2.2.4 we were just clicking in the box next to hidden but in 2.2.9 we need to enter the appropriate number. I have tried several options but did not manage to connect the authority to the field. Does anybody know what I need to do? Thank you in advance for any replies. Georgia Library & Information Service DIKEMES/ College Year in Athens Plateia Stadiou 5 116 35 Athens, Greece TEL +30 210 7560749 (121 ext.) FAX +30 210 7561497