To reverse a transactions using corrections:
Click Debtors then click Customers.
Select Transactions.
Right click on the transaction then click Correct.
Select either Reverse as Negative Transaction or Reverse as Opposite Transaction.
Select the date, period, and year the reverse transaction requires posting too.
Select Batch Transaction and enter the Batch Ref.
Enter a Header Ref then select the green tick.
Click Yes to the prompt then click OK.