In the first instance please call them to discuss the changes. If it's possible to accommodate them, they'll be happy to help. Please note that once confirmed, bookings can only be moved to an earlier date. Helpful Holidays are not able to change a booking to a later date.
Changes to an already booked holiday involve extra administration and require them to contact the owner of the holiday property. To cover these additional costs they ask the holidaymaker to pay an administration fee of £30.