Problem controlling fan speed with potentiometer AND temp sensor

Hey! im really new to arduino and i have a project where my fan speed changes by the temperature.
i want to add a switch so i can change it manually or automatic. could somebody please help me with this =( my code looks like this :
LiquidCrystal lcd(12,11,5,4,3,2);
int tempPin = A0; // lämpösensorin pin LM35
int fan = 10; // tuulettimen pin 10
int fan2 = 9; // tuuletin 2 pin 9
int led = 8; // ledin pin 8
int temp;
int tempMin = 20;
int tempMax = 70;
int fanSpeed;
int fanLCD;

void setup() {
pinMode(fan, OUTPUT);
pinMode(led, OUTPUT);
pinMode(fan2, OUTPUT);
pinMode(tempPin, INPUT);
lcd.begin(16,2);
}

void loop() {
temp = readTemp();
if(temp < tempMin) {
fanSpeed = 0;
digitalWrite(fan, LOW);
digitalWrite(fan2, LOW);
}
if((temp >= tempMin) && (temp <= tempMax)) {
fanSpeed = map(temp, tempMin, tempMax, 32, 255);
fanLCD = map(temp, tempMin, tempMax, 0, 100);
analogWrite(fan, fanSpeed);
analogWrite(fan2, fanSpeed);
}
if(temp > tempMax) {
digitalWrite(led, HIGH); i
} else {
digitalWrite(led, LOW);
}
lcd.print("TEMP: ");
lcd.print(temp);
lcd.print("C ");
lcd.setCursor(0,1);
lcd.print(“FANS: “);
lcd.print(fanLCD);
lcd.print(”%”);
delay(2000);
lcd.clear();
}

int readTemp() {
temp = analogRead(tempPin);
return temp * 0.48828125;
}