Insert a button in programming Help!

Hello guys, I'm still a beginner in the language and I'm looking for some help on this, insert a button on the pin 11 so that clicking it Microservo the return to the starting position, as you can do this? another problem is that the Microservo "vibrates" because I believe that you do not in the ideal position, how do I resolve this? help guys.
Giacomo.

#include <Keypad.h>
#include <Servo.h>
#define LED 13 //  Green Led
#define LED 12// Red Led
int Buzzer = 9;
Servo myservo;

const byte ROWS = 4;
const byte COLS = 3;
char keyInsert[5];
int i = 0;
int j = 0;
int s = 0;
int x = 0;
char code[5] = "1997";
char keys[ROWS][COLS] = {
  {'1', '2', '3'},
  {'4', '5', '6'},
  {'7', '8', '9'},
  {'*', '0', '#'}
};
byte rowPins[ROWS] = {8, 7, 6, 5};
byte colPins[COLS] = {4, 3, 2};

Keypad keypad = Keypad( makeKeymap(keys), rowPins, colPins, ROWS, COLS );

void setup() {
  Serial.begin(9600);
  pinMode(12, OUTPUT);
  pinMode(13, OUTPUT);
  pinMode(9, OUTPUT);
  myservo.attach(10);
}

void loop() {  //insert PIn to verify
  char key = keypad.getKey();
  if (i == 0) {
    i++;
  }
  if (key != NO_KEY && j < 4) {
    Serial.print("*");
    //Serial.println(key);
    keyInsert[j] = key;
    j++;
  }
  if (key == '*') {  // Verifyng the code
    delay(100);
    for (s = 0; s < 4; s++) {
      if (keyInsert[s] == code[s]) {
        x++;
      }
    }
    if (x == 4) { //Password Correct
      Serial.begin(9600);
      digitalWrite(13, HIGH);
      digitalWrite(9, HIGH);
      delay(50);
      digitalWrite(9, LOW);
      delay(100);
      delay(400);
      digitalWrite(13, LOW);
      myservo.write(0);
      delay(1000);
    


    } else { //Password Wrong
      digitalWrite(12, HIGH);
      delay(400);
      x = 0;
      i = 0;
      j = 0;
      digitalWrite(12, LOW);
    }

  }
  if (key == '#') {
    x = 0;
    i = 0;
    j = 0;
  }
}

I have a servo that vibrates around 0-20 degree range and near 180. Is your servo also vibrating around these ranges?

I suggest you study the example->02.digital->Debounce in arduino. Keypad is NOT what you want.

      Serial.begin(9600);

Conditionally, in loop()? Why? This belongs in setup().

How are you powering the servo? Incorrectly is my guess.

I solved the problem of the servant that "vibrates" the problem was not just plain a stable supply. For how can I fix the problem button, someone who knows how to implement a button inside the skatc?

For how can I fix the problem button,

What is the problem? Aside from the fact that you don't appear to actually be reading pin 11.

I would insert in the sketch of a button that when pressed moves the servo starting position

SlicedStream:
I would insert in the sketch of a button that when pressed moves the servo starting position

I have no idea what that means. A "button" (more correctly known as a switch) is a piece of hardware. You don't insert hardware in a sketch. You wire up hardware. You read the state of the switch in the sketch.

Have you wired up the switch? If so, how? If not, how can you expect to read the state of the switch?