Hello @Sg0,
I'm not sure what you've already tried. Some suggestions ...
If someone has already booked those dates you won't be able to change the price by selecting the dates on your calendar.
In that case you'll have to go to "Host", "Your reservations", find the reservation and request athe guest to agree to the price change by clicking on "Change or cancel".
If no one has yet booked the dates have you tried the following?
Go to your calendar and click on "Manage listings" in the top right hand corner. Then select "Pricing". Then select "Edit" in the "Discounts" section and scroll down to set a custom weekly or monthly price.
You should also be able to go to your calendar and select the first date of a range. Then, in the window on the right select the start and end dates and set the price. Remember to click on "Save changes".
Steve.