A Prepay Check can be both printed and voided through the unposted Items screen. This screen can be opened by clicking 'Unposted Items' in the 'Recent Payroll Activity' tile of the Payroll console.
When the 'Unposted Items' screen loads, a listing of all unpaid Prepay Checks will be listed. Next to the Employee name, click either 'print' or 'void', depending on the desired action.