Maybe something like this would work? I haven’t actually tested it, but hopefully this gives you something to start from. Let me know if you are still having difficulty - or if I misinterpreted your question - and I can try to refine it.
Another workflow that might be of use to you is available on the Workflow Hub here: https://workflows.knime.com/knime/hub/workflows/06_Control_Structures%3A04_Loops%3A05_Write_each_row_in_one_file
(You can find it on the EXAMPLES server too)