Add console.log() and debug what parameters are you sending as well as what response you get?
Can you explain what are trying to achieve?
where is detials field. If this is a field from your parent form then you have to iterate child table entries to set values in every row of the table.
e.g.
frappe.ui.form.on("Registration",{
detials: function(frm) {
$.each(frm.doc.tablefieldname || [], function(i, v) {
frappe.model.set_value(v.doctype, v.name, "email", "xyz@gmail.com")
})
}
})