If you logged some food into one of your daily meals (for example, into breakfast) by mistake and want to delete it, there are several ways to do that.
On Android, you can quickly swipe the entry to the right or left, and it will be deleted. On iOS make a short swipe from right, so that action buttons will be displayed for this food entry, including Delete.
Another way is to tap and hold the food entry to open the editing screen, then tap "Delete Food Entry" at the bottom of the screen on iOS or the top of the screen on Android.
Finally, if you want to delete or move several food entries, you may want to use the "Copy/Move/Delete" feature, accessible after tapping "3 dots" in the upper right corner on both iOS and Android. The meal screen will switch into editing mode, and you will be able to select several food entries and delete or move them as a group.