The delete button is the red button with the white left pointing arrow (above the Wicket button). This button deletes the last event that was scored such as a dot ball, extra, runs, wickets, retirements etc. If you press it before any balls have been scored in the over it will take you back to the previous over with the app asking you if you want the over to be completed. If you wish to delete balls in that over, select no and you will be able to delete every ball in that over if you wish. If you press the delete ball button at the beginning of an innings, you will be given the options Reset innings, which will take you to the new innings page where you will select the facing and non-facing batsman for the start of the innings again, and the opening bowler and wicket keeper. Alternatively you can select Return to Previous Inning which will mean you can edit and delete any ball from that innings. The other option is the cancel button which will take you back to the scoring screen.