Can my customer edit their return request?
As long as your team have not reviewed the return request, your customers are allowed to edit their return request by simply clicking on the 'Update' button after inputting their order ID and email address.
After the return request has been reviewed, your customers would not be able to edit their request. Any editing will have to happen offline to prevent any mix-up / miscommunication between you and your customer i.e. customer requesting to exchange for a different item after the item has been shipped.
For those who have the automated approval enabled in their 'Return Settings', you can always delay the approval by your preferred number of hours. For example, you can delay the approval by 48 hours so that your customers will have more than sufficient time to make changes to their return request if needed.