You can perform the refunding of Walmart's orders directly in Listing Mirror!
First, let's look at the correct workflow.
To do so, select Show Returns from the Orders drop-down menu.
Next, click on details of the order you want to perform the refund on.
This is the Return Details page.
From here, you can choose to refund the return as is, or you can choose to set your own return options.
When overriding standard return options, you can choose to charge for shipping and restocking fees. If you include those fees, you will need to add the reason for doing so under Override Reason.
Lastly, here is an article from Walmart's knowledge base about their Return Process