At the moment availability for your listing seems to be set to 3 months in advance so I presume you're asking how to set availability for the golf next year without also making it available for all the dates from now until then.
If that's the case, then just go to your calendar and click on the first date you want to make available for the golf. A window will appear on the right. In the "Selected dates" box click to the right of the arrow and enter the last date you want to make available. Then click "Available" and then make sure to enter a price for these nights. After you've entered a price click on "Save".
I am still finding it difficult , I can fix dates but I don't want house let out on a nightly basis but for the duration of the tournament so I don't want to do a nightly price. The calendar won't let me do this. Also I'd like to know how I specify that it's available for the golf?
What you might want to do, @Jenny560, is go to Listings -> Edit -> Availability, and then hit Edit beside Reservation Preferences. In the Booking Window, choose "Dates unavailable by default". That blacks out all your dates, and then you can go to your calendar and open up the specific dates you want for the golf.
Also, in your listing summary, you can say something like "This listing is available only for the Royal Portrush Open."