How can I add 'applies to invoice #' in Crystal Reports for customer credits?

SOLVED

We had our system put in about a month ago(Sage 100 2021). When I go to make a customer credit in the Sales Order module, I can apply it to a specific invoice. But once I go to send the customer the credit, nowhere on the form is there a 'applies to invoice #:'(at least that I can find). So even though the credit applies to a specific invoice, our customer thinks it is just an open credit. I'm not great with the formulas since I'm so new. Can someone please tell me how to get this to come up in Crystal Reports?

Thank you in advance for any help!!