The closest term I can find is "return order", but I feel that it's very similar with "repeat order", so I'm afraid it has a double meaning.
"Return" is the correct word. "Return" is a verb. We say, "The customer returned the product". We DO NOT call it "a return order". You can call it "a returned item" or "a returned product", or simply "a return".
Yes, a "repeat order" is ordering the same thing again, ordering something you had previously ordered again. There is no ambiguity with "return". We do NOT say "a return order" to mean ordering the same thing again. I suppose you could say, "The customer returned to the store and bought the same item again", but it would be "returned to the store [or, our web site] and made a repeat order", NOT "made a return order".
I'm not saying that I'm one hundred percent sure whether this is the precise term they use in the business world, but purchase return is what instantly came to mind when I saw your post:
A purchase return occurs when a buyer returns merchandise that he or she has purchased from a supplier.
Another similar term would be product recall, but product recall usually only applies to situations where products are returned (or recalled) to the supplier on a mass scale typically due to the discovery of some sort of serious defect or problem in them:
A product recall is a request to return a product after the discovery of safety issues or product defects that might endanger the consumer or put the maker/seller at risk of legal action.