Elias here with Shopify Support. That’s a great question!
There are a few third-party apps that can help with return management, allowing your customers to start their returns directly on your store - even if they aren’t registered for a customer account. However, I’m not having much luck finding one that allows customers to edit their own orders. That being said, I can imagine allowing customers to edit their own orders may create more problems, especially from a fulfillment standpoint. I’ve handpicked a couple of return management apps for you to try out:
If you need any help with these apps, you can always reach out to the developers directly through the contact information found in the Support section of their app’s page.
I hope this provides a few options for you to explore. If you have any further questions on return management, feel free to reply back to this thread and I’d be happy to help.