If you accidentally responded No to a request, then it is impossible to get the ILL request back to your Message File (Request Manager). The request is on its way to either the next lender or back to the borrower as an Unfilled request.
If you responded
Yes when you meant to say
No, then there's still a chance to correct your error. If you haven't done a
Replace command or exited the record, then you can use the
Recall command and type a note of explanation in the
Lending Notes field. You may also need to contact the borrower to explain the situation.