The numbers can be freely edited one by one after entry. Tap the number you want to edit to enter edit mode.
The number in focus can be updated by tapping the number button. You can also use the arrow buttons to move the focus of the number.
Tap the Delete button to delete the number with focus
Tap the number in focus or tap the check button in the lower right corner to deselect the number.
The operator of a formula can also be selected by tapping it and can be edited in the same way.
To delete a row swipe left on the row to be deleted and tap the Delete button.
If you want to set the entire formula in this case 23456 + 789 to 0, tap the lower left button then tap Delete all current formulas.