Use merge tags to populate dynamic information in notification emails

Under WP Admin > BookingRobin > Settings > Emails, you may edit email notification templates to both providers and clients by adding proper merge tags. 

You may find all system merge tags  here.

To find the merge tags of added custom fields, go to WP Admin > BookingRobin > Settings > Form builder, click on the field, on Field setting section at the left of the page, find Field ID there. For instance, if the field ID is field2, its merge tag is {{field2}}.