It is possible you want to modify supplements for specific dates, you can create supplements by season selecting the tab Exceptions:

1. Click +Create exception.
2. Select the supplement already created to create the exception
3. Select the date interval you want to modify. You can add more than one interval or select specific days of the week to apply.
4. How is the supplement applied? Charged by room/night or by stay.
5. Include the default value for the supplement, it can be an increment or decrement of the price.