update.kt

val person = Person(
                null,
                etName_firestore_update.text.toString(),
                etEmail_firestore_update.text.toString(),
                etPhone_firestore_update.text.toString())

db.collection("Person").document(personExtra.id!!).set(person)
                .addOnSuccessListener {
                    "Updated Successful.".toast(this@UpdateFirestoreActivity)
                    finish()
                }.addOnFailureListener { exception ->
                    "Error: ${exception.message}".toast(this@UpdateFirestoreActivity)
                }