Combo products get their availability from the products they are based on. So if e.g. a Horse Riding trip, that is a base product in your combo product is sold out the combo product is sold out.
You have one option to manage the availability for you combo product, by closing days. E.g. maybe you don't want your combo activity to be available on certain dates, then you can close those dates on the combo tour. The base tours will still be bookable individually.
To close dates, select the "Close out" tab on your product:
On this page you get an overview of all departures per day, you always default on the date today when you enter this page.
To close a full day or a departure, select the day from the calendar on the right hand side of the screen.
To close a day select the green toggle button by the booking count label.
To close a departure select the green toggle button by the correct departure.
When the green toggle button is selected it turns grey, which means that the date /departure is closed.
To open the departure again just select the toggle button again, then it will turn green and the date is open again.
When you close a date, the date will appear as red an will be un-bookable in your booking engines.
If you close a single departure, that denature will be closed for bookings, but the customer sees the day as open and can book the other available departures.