I started by running the I2C address scanning (Red code)

Scanning…
I2C device found at address 0x01  !
I2C device found at address 0x02  !
I2C device found at address 0x03  !
I2C device found at address 0x04  !
I2C device found at address 0x27  !
done

Sunfounder LCD 20×4: I2C device found at address 0x27 !

Each I2C LCD screen has three pads: A0, A1, and A2.  Below is the table that shows how to solder the pads to change the address.   Below the table is a picture of the I2C LCD screen pads on the right side.   Soldering them can be tricky to do.  

A0A1A2Hex
openopenopen0x27
closedopenopen0x26
openclosedopen0x25
closedclosedopen0x24
openopenclosed0x23
closedopenclosed0x22
openclosedclosed0x21
closedclosedclosed0x20

// Include the required Wire library for I2C
// Include the libraries:
// LiquidCrystal_I2C.h: https://github.com/johnrickman/LiquidCrystal_I2C
#include <Wire.h> // Library for I2C communication
#include <LiquidCrystal_I2C.h> // Library for LCD

// Wiring: SDA pin is connected to A4 and SCL pin to A5.
// Connect to LCD via I2C, default address 0x27 (A0-A2 not jumpered)
LiquidCrystal_I2C lcd = LiquidCrystal_I2C(0x27, 20, 4); // Change to (0x27,20,4) for 20×4 LCD.

#include <Wire.h>
int x = 0;
int LED = 13;

void setup()
{
 
 // Initiate the LCD:
  lcd.init();
  lcd.backlight();

// I2C counter for LEDs  
pinMode (LED, OUTPUT);
// Start the I2C Bus as Master
Wire.begin();
// I2C counter for LEDs  

/*
// I2C Scanner Code
Serial.begin(9600);
while (!Serial);             //  wait for serial monitor
Serial.println(“\nI2C Scanner”);
// I2C Scanner Code
*/

}

void loop() {
 
//LCD I2C 20X4
lcd.setCursor(3, 0);    // 4th column 1st row
lcd.print(“Welcome aboard”);
 
lcd.setCursor(8, 1);    // 9th column 2nd row
lcd.print(“the”);
    
lcd.setCursor(6, 2);    // 7th column 3rd row
lcd.print(“Heart of”);

lcd.setCursor(2, 3);     // 3rd column 4th row
lcd.print(“Stainless Steel”);
//LCD I2C 20X4

// I2C counter for LEDs    
x++; // Increment x

//From Left to Right
// First UNO
Wire.beginTransmission(1); // transmit to device #1
Wire.write(x); // sends x
Wire.endTransmission(); // stop transmitting

//Second UNO
Wire.beginTransmission(2); // transmit to device #2
Wire.write(x); // sends x
Wire.endTransmission(); // stop transmitting

//Mega in the Middle

//Third UNO
Wire.beginTransmission(3); // transmit to device #3
Wire.write(x); // sends x
Wire.endTransmission(); // stop transmitting

//Fourth UNO
Wire.beginTransmission(4); // transmit to device #4
Wire.write(x); // sends x
Wire.endTransmission(); // stop transmitting

if ( (x == 3) || (x == 6)) {
digitalWrite(LED, HIGH);
}
else {
digitalWrite(LED, LOW);
}
 
if (x == 7) x = 0; // `reset x once it gets 6
delay(1000);
// I2C counter for LEDs  

/*
// I2C Scanner Code
byte error, address;
  int nDevices;
 
  Serial.println(“Scanning…”);
 
  nDevices = 0;
  for(address = 1; address < 127; address++ )
  {
    // The i2c_scanner uses the return value of
    // the Write.endTransmisstion to see if
    // a device did acknowledge to the address.
    Wire.beginTransmission(address);
    error = Wire.endTransmission();
 
    if (error == 0)
    {
      Serial.print(“I2C device found at address 0x”);
      if (address<16)
        Serial.print(“0”);
      Serial.print(address,HEX);
      Serial.println(”  !”);
 
      nDevices++;
    }
    else if (error==4)
    {
      Serial.print(“Unknown error at address 0x”);
      if (address<16)
        Serial.print(“0”);
      Serial.println(address,HEX);
    }    
  }
  if (nDevices == 0)
    Serial.println(“No I2C devices found\n”);
  else
    Serial.println(“done\n”);
 
  delay(5000);           // wait 5 seconds for next scan
// I2C Scanner Code
*/

}