First you need to send your new data to backend
in fronend_booki.js
fiind .
exports.updateConfirmFrame = function () {
add your new field to
customcheck: $('#
customcheck ').prop('checked'),
}
or you can add it to data.appointment = { depend on type of the data
now you need to add this field in back end
if this related to customer info you need to add it in Customers_model insert function
if its related to appointment you need to add it in appointments_model insert function
remember you need to add the new field also in the database