Yes, this can be accomplished in the Registers screen. 

1. From the main menu, open Accounting > Registers.
2. Select the Register from the drop-down that you want to undo the reconciliation for.
3. From the more menu, click Reconcile.
4. On the Reconcile Accounts dialog, click Manage Reconciliations.
5. Core displays the account reconciliation history. Click Actions > Undo.
6. Core notifies you of the effects of this action on your account. Click Confirm.

Check out this article on Bank reconciliation in Core.