Lock box Receipt application to a customer with reciprocal relationship

The customer account A was the parent and Customer B was set up as the child of the customer A with reciprocal relationship. A payment was received from parent account A (Remitting customer A) listing the invoice numbers of both A & B to be applied via lockbox. Due to invalid invoice numbers on some of the lines of receipt, it got posted as On account to child customer B. But, We wanted it to post to the remitting customer/Parent account A. Please help how can we make the On account cash to be on parent customer instead of the