Once a reconciliation has been posted it is in stone and you can no longer reverse the checks. If it is a matter of moving balances around you can post an AR adjustment to the customers AR invoice in order to open it back up to receive payment. This will update AR and the GL but not the bank so you will also need to post a bank entry bank withdrawal that uses the same GL account as the bank.

You can change the status from Reconciled to Open by doing the following:

go to Cash Management

Tasks:  Edit Register

Find the transaction and click on the three dots with arrow (towards the right of the screen)

Chang the status from "R" to "O"

Once you change the statuses to Open, you can fix your errors. Afterwards, you can go back to the Reconciliation and use the month of April again to clear the correct transactions.

Sage 300cloud (AKA Accpac) doesn't have a Cash Management module.  You may be referring to the other Sage 300 product.