Adding Button To This Code

I want to add a button to open the door. Help me out please guys im a starter for this Ardu universe.

NOTE: This is a keypad door lock project.

#include <Servo.h>
#include <Keypad.h>
#define buzzer A0

Servo ServoMotor;
char* password = “5620”;
int position = 0;
const byte ROWS = 4;
const byte COLS = 4;
char keys[ROWS][COLS] = {
{‘1’,‘2’,‘3’,‘A’},
{‘4’,‘5’,‘6’,‘B’},
{‘7’,‘8’,‘9’,‘C’},
{’*’,‘0’,’#’,‘D’}
};

byte rowPins[ROWS] = { 8, 7, 6, 9 };
byte colPins[COLS] = { 5, 4, 3, 2 };
Keypad keypad = Keypad( makeKeymap(keys), rowPins, colPins, ROWS, COLS );
int RedpinLock = 12;
int GreenpinUnlock = 13;

void setup()
{
pinMode(buzzer, OUTPUT);
pinMode(RedpinLock, OUTPUT);
pinMode(GreenpinUnlock, OUTPUT);
ServoMotor.attach(11);
LockedPosition(true);
}

void loop()
{
char key = keypad.waitForKey();

if (key == ‘*’ || key == ‘#’)
{
position = 0;
LockedPosition(true);
tone(buzzer, 1000);
delay(50);
noTone(buzzer);
}

if (key == password[position])
{
position ++;
tone(buzzer, 500);
delay(100);
noTone(buzzer);

}
else if (key != password[position])
{
position = 0;
tone(buzzer, 500);
delay(100);
noTone(buzzer);
}

if(position == strlen(password)){
LockedPosition(false);
delay(100);
tone(buzzer, 1500);
delay(100);
noTone(buzzer);
delay(10000);
tone(buzzer, 100);
delay(50);
noTone(buzzer);
LockedPosition(true);
}
delay(100);
}
void LockedPosition(int locked)
{
if (locked)
{
digitalWrite(RedpinLock, HIGH);
digitalWrite(GreenpinUnlock, LOW);
ServoMotor.write(11);
}
else
{
digitalWrite(RedpinLock, LOW);
digitalWrite(GreenpinUnlock, HIGH);
ServoMotor.write(90);
}
}

Look here

TolpuddleSartre:
Look here

Yeah, the OP cross-posted!

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