I mistakenly left(not entered) my "response" for a refund case. How to edit it, any solution?

[ShubhamKr_IND]

A guy (my customer) has filed a fake case for a refund of the service I offered to him.

In the resolution centre, I was asked to put my response. But, mistakenly I clicked on the save button without actually writing my response.

Now, my response is showing Null.

Please tell, how can I edit that response? And, how to prevent the refund for the service I actually gave to my customer?