With the online system, you can quickly search for available dates or make cancellations to existing appointments at the Bibbidi Bobbidi Boutique locations in domestic U.S. Parks, and at The Pirates League and Harmony Barber Shop in Magic Kingdom Park at Walt Disney World Resort.
The site will seem familiar to anyone who has made an online dining reservation as it contains a similar layout and features (just create or sign into your Disney account to get started).
Guests are strongly encouraged to make reservations in advance for these experiences as they are quite popular and appointment times fill up quickly. Reservations can be made up to 60 days in advance for the Bibbidi Bobbidi Boutique (ages 3-12) in Disneyland park. At Walt Disney World Resort, reservations can be made up to 180 days in advance for the Bibbidi Bobbidi Boutique (ages 3-12), The Pirates League, or Harmony Barber Shop.
Link to WDW does not work, online booking for these are nowhere to be found on the WDW site as of yet.
Disney provided the link, I sadly can’t provide tech support for them.