It's very easy.


iOS

Swipe left on the flight you want to delete.



Then tap red button to delete.



Android

Tap and hold the flight you want to delete. If it's a one-leg flight, you would see a delete button at the top right-hand corner. 



If its a multi-leg flight, tap and hold, and then select the "3 dots" at the upper right-hand corner and select "delete".



Select "Delete".