How to configure [click2approve], [click2decline] and [click2trash] shortcodes ?

Such shortcodes possible to use in the Booking > Settings > Emails page in New (admin) email template only.
Available since update 8.5.1 of paid versions of Booking Calendar.

Using of such shortcodes require correct configuration of [bookingedit] shortcode in your system.
Please check this FAQ instruction how to configure it.