How to retire an 'Expense' of Employee who has left the company

Hello team

We have a user who has raised an expense and has left the business. Insignificant amount, no longer with business or whatever, the amount has been rejected by the approver. Currently if I look at the workflow history, it is parked with the ex-employee and the Document Status is “In Review”. We would like to retire this expense as our “In Review” reports are being skewed by such aged expenses. If I re-assign to another user for them to reject, the error message I am getting is “User XXXX not found”. XXXX being the ex-employee.

So how best to retire this expense AWAY from “In Review” status? (We don’t want to delete the expense fully with no trace for audit purposes nor bring back the user into the Active Directory). Any other way to cancel / reject the expense from the front end? If not, how do we do it from the back end? Any info I can give my tech would be useful.

Thank you