The Product Reference ID found in the eBay edit listings page is a field in use when you're using Catalogue Listings within eBay. The Product Reference ID is the market ID for the catalogue listings itself.
If you need to remove or change the catalogue listing your eBay listing is pointing to, you can remove or change the market ID from the Product Reference ID field when editing the eBay listing! It is found directly below the description, template, and category fields!
If you have any questions about the product reference ID or eBay catalogue listings, please reach out to support!