How do I reverse an Áccepted Return?

I have had a buyer put in to get a return but they wanted a replacement which I have sent and have proof of postage for.
My issue is that  have just sent them a final message with the details & some how when the message finished the original screen was there where you can choose an option to Accept the return, Send a message etc & I have accidently clicked the submit button & it started a return.
There is no back button & I can't get it to go back to how it was.
Can anyone help me cancel the selection I have made??
Help please I am deperate......