It is not necessary to settle the balance due on an electronically filed return by direct debit.  If your client doesn't have a bank account, he/she may purchase a money order and send it in with a conventional payment voucher on paper.  If your client has access to a credit card or debit card, payment can also be made online except there will be a convenience fee.

https://www.tax.ny.gov/pdf/current_forms/it/it201v_fill_in.pdf

https://www.tax.ny.gov/pay/all/make_a_payment_section.htm