https://help.myob.com/wiki/x/1Iii
To delete a previous year's transaction, you need to write a new transaction to the same code. This cancels out the original amount.
For example, if you originally had a cheque for $10 to code 200/01, you would write a deposit for $10 to code 200/01.
When reconciling, you'll need to reconcile both transactions.
Cashbook user guide
