You can easily exclude a round from statistics and even add it back to your statistics if you change your mind. It is available from round details at the end of the round or from playing history (start screen > playing history > select the round). Just check the box at the bottom of the screen to include a round or un-check it to exclude. If you exclude a round, the round results will be excluded from your statistics.
Note: this feature is currently available in version 14.42.1 or later for Android. iPhone will be released in the future.