@Sophocles0 That is so odd, I just checked on my iPad and you're absolutely right. When you go to Booking Settings -> Pricing, you can see your discounts under "Length-of-stay pricing." But when you click through, there's no way to edit them.
The only thing I can see is "Add a custom length-of-stay discount." Then you get the option to choose a number of nights from 2 through 6, or 14. (This may be because I already have weekly and monthly discounts chosen. Perhaps if I hadn't you'd get the option to choose from 2 through 30.)
No ability to edit is so strange!