Yes, there is a utility to reverse slips and expenses written off.  Go to  Setup/Utilities>General Utilities>Reverse Slip/Expense Write-offs .  The only information needed other than the client’s name is the date that the timeslips were written off (determined by the date on the dashboard not the calendar date).  If you do not know the date then run the  Client Time History Report for written off slips\expenses (see settings below).