You can either have cancelled bookings stay in your diary marked in grey, or if you want them to disappear. If they are still showing in your diary, the availability will be shown on your online booking if it is more than 10 minutes in the future

This is a user based setting so if you have multiple users each one can have this set for them individually

Click Options in the top right of the diary -> Toggle 'Hide cancelled bookings' on or off -> Update