Customer Return for Credit

I am trying to create a Return for Credit for one of my customers. Usually I am able to attach/link an invoice to the RC and add the item so it returns back to my inventory. However, this particular customer/invoice does not populate the product that needs to be returned back to inventory. Does anyone have a suggestion or is there something I may be missing. I don’t want to just add the item without linking the invoice and then I end up messing up inventory or have issues refunding my customer when I do the Credit Memo.