How do we use a credit listed on one Job to a different job with the same customer?

How do we use a credit listed on one Job to a different job with the same customer?

 We are using Quickbooks Enterprise Version 7.0.. We get one check from the restaurant management company paying for multiple restaurants. They sometimes take credit on this master check on an account that they are not paying invoices for. The individual restaurants are listed in QB7.0 as jobs under one master account.

Thanks