It's very easy on both of the platforms. Please follow these steps.
Swipe left on the flight you want to delete.
Then tap the red button to delete.
Tap and hold the flight you want to delete. If it's a one-leg flight, you would see delete button at the top right-hand corner.
If it's a multi-leg flight, tap and hold, and then select the "3 dots" at the upper right-hand corner and select "delete".