Any unfilled portion of an order can be canceled. To do so, tap on the unfilled or partially filled order from your Trade screen.
This brings up the order details screen. Tap the Cancel Order button at the bottom of the screen to cancel any portion of the order that remains unfilled. In the example used in this article, the order is 0% filled, so tapping on Cancel Order will result in 100% of the order being canceled.
You will be brought back to the Trade screen and an order cancellation confirmation will briefly be shown at the top of the screen.