Declined
Undo a Card
I have not found any way to undo a card on iOS. I would say that it is quite the necessary feature, especially when dealing with misclicks.
For example, missing the toggle button for correct and wrong will completely mess up the card SRS, which could be fixed with an undo option.
Or, when accidentally tapping the screen and messing up the drawing, you could choose to go to the next card, undo, and try again.