You can cancel any Pending order in Zentail. 

1. On the left sidebar, click on "Pending" then search for and click on the order you wish to cancel.
2. On the left slider that appears => Click the 3-vertical-dot icon at the top of the page => Click "Cancel Order".
3. If you do not want to return quantity to stock "uncheck" the box that says "Return Quantity to stock" on the subsequent pop-up message.