You will need to first void the Invoices created  (TARGETS ONLY…NEVER VOID THE INVOICE NUMBER ASSOCIATED WITH THE SOURCE).  Once the Invoices have been voided, go into Bill Prep and enter the “source” Client-Matter (you will receive an information box that there are no fees/costs matching the criteria), click OK. Click on Tools > Reverse Split Billing. Enter the Client-Matter (source) and “Show Splits.” Highlight the item based on the “split-date” and choose “Reverse Split” (this will place the WIP back on the source Client-Matter).