From the Appointments tab, go into your Online booking settings Tab 2, Bookings Settings and Customisation.
Below where you choose the colour scheme for your Online booking page there is an option and box titled Success Message.
Customise the confirmation message you would like to display once the booking is made successfully.
Add a URL link (Callback URL) to any page you would like your clients to be sent to 5 seconds after they complete
Example: Send clients to your Social Media page or your website
Once finished press the green Save settings top right.