You will not be able to move it to the correct matter in Expense Entry. There are two ways you can handle this issue:
1. You can adjust the voucher. Delete the distribution to the wrong Client-Matter, and add the distribution to the correct Client-Matter. Pay attention to your date and period during the adjustment process. If your system has been advanced to the current Period, the adjustment will default to the current Period and Date.
2. In Bill Prep, move the entry to the correct Client-Matter.