You basically work backwards deleting out the offending transactions which will in turn create reversing jnls in the accounting package

Recall the Customer Payment (ticking the include fully applied status).

From the Detail screen of the payment, click on the History tab at the bottom. This will show you the invoices the payment was applied to.

Click on each invoice and press the Delete button (Right Hand side of screen) to delete each application.

   This will DR Debtors and CR Unapplied Payments. As you do this, you will notice that the payment Status changes. You can then re-apply the payment to the correct invoices on the account or go to    the next step to delete the entire batch........

....Once you have deleted all applications, go to the list screen and delete the payment batch. This will DR Unapplied Payments and CR Bank

The dates of these jnls are controlled by how your Sales Rules are set for the following:
Applying Payments Date
Payment Deletion Date