Dependent on what has happened on the file if the TOC has been billed or allocated then you won't be able to just reverse the TOC posting.
This is done by:
From the Main Menu go into General Postings and select the TOC type.
Select the Reversal box and then select the posting to reverse in the allocation box.
If allocations exist then the transaction that has been allocated to it would need reversing first and then you can reverse the TOC, or do a minus TOC marked as a disbursement and a positive TOC not marked as a disbursement.
If the TOC has been billed then the same contra postings can be done and create a SIB for the minus TOC then allocate against the bill.
If the receipt has come in for the bill then this can just be allocated to the matter and another TOC done not marked as a disbursement to post over to the client ledger as it is an overpayment and no longer needed.