How to push the Selection of a UIPicker to Firebase - swift

Question

how can I push the User Selection of a UIPicker to Firebase Database? So for example he hit on "male" than it will be stored in the Firebase Database...
My code for the UI Picker
class AddExtraData: UIViewController, UIPickerViewDataSource, UIPickerViewDelegate {
func numberOfComponents(in pickerView: UIPickerView) -> Int {
1
}
func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
return data.count
}
func pickerView(_ pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {
return data[row]
}
#IBOutlet var pickerView: UIPickerView!
let data = ["male", "female", "else"]
override func viewDidLoad() {
super.viewDidLoad()
pickerView.dataSource = self
pickerView.delegate = self
}
EDIT:
Database
Here is my database.
Now I want to get to write the data which is stored in seclectedYearPicker to the database.
var ref: DatabaseReference!
ref = Database.database().reference()
let selectedYearPicker = data[pickerView.selectedRow(inComponent: 0)]
print(selectedYearPicker)
let userID = Auth.auth().currentUser!.uid
ref.child("users").child(userID).setValue(["gender": selectedYearPicker])
}
If I make this, there will be a new dataset:
let db = Firestore.firestore()
db.collection("users").whereField("uid", isEqualTo: Auth.auth().currentUser?.uid ?? "x")
.getDocuments { (querySnapshot, err) in
if err != nil {
print("Failed")
return
}
let userdocid = querySnapshot!.documents[0].documentID
db.collection("users").document(userdocid).setData(["koordinaten" : selectedYearPicker])
}