[Koha] import items

Hi, I've imported my bibliographic records and want to add items. For bibliographic records, i've added 995 field and subfields. My items are in another marc file but i don't know how to link both. Something i don't understand is, when i am in stage marc records for import, the item "record matching rule" is fixed on "do not looking for matching records". I can't choose another solution. That would may be the reason i can't link bib and items records? I've not tested with bulkmarcimport for the moment. best regards samuel