We understand plans can change. So if you need to change the date and time of your booking, contact us https://www.getyourguide.com/contact and we'll do our best to update your booking.
Unfortunately due to security reasons, we cannot add people to your booking. We fully encrypt your payment details, so cannot take money from the account to add another person to your original booking.
However, you can easily add another person by making a separate booking for the exact same date and time.