Import to Subform

Import to Subform

I have a forrm with subform. I managed to prepare import that creates new record (in main form) and also creates 2 records in subform. it works just fine.
Here is my problem, I need to import subform records to already existing main records ( none of them currently have any records in subform). It does not work.
The way I tryed it: I used "ID"  field of the main record, this record is updated, however it does not create records in subform