After the activity has started, you still have the option to:
Add extra days to, or
Remove days from your activities after bookings have been taken on that activity
Important note:
Your customers will not be automatically booked into these Extra Days
Please encourage your customers to modify their bookings
How To Add Days To Your Activity
Navigate to the activity
Click Edit Activity
Go to the Day Confirmation section
At the bottom, in the Insert Extra Day section, click the Select Day box. Choose the date you wish to add
Click Add Additional Day
Save your new settings