I have issue adding a sorting function, please guide?

1. Write a program that would print the information (name, year of joining, salary, address) of employees by creating a class named 'Employee'.
2. Create a function in the Employee class that finds an employee by the given year of joining.
3. Create a function for sorting the employees according to their given year of joining.
4. Create a Display Function for Employee Class.

This is what i was asked you make, i coded everything possible, but was unable to implement this part "Create a function for sorting the employees according to their given year of joining." can someone guide me how to add this? i am having trouble while doing so.

This is what i coded so far

#include <iostream>
#include <string>

using namespace std;

class Employee{
    private:
        string name;
        string address;
        int year;
        int salary;

    public:
        Employee(string, int, int, string);
        string getName();
        int getYear();
        int getSalary();
        string getAddress();
        void displayData();
};
Employee::Employee(string n, int y, int sal, string add)
{
    name = n;
    year = y;
    salary = sal;
    address = add;
}
string Employee::getName()
{
    return name;
}
int Employee::getYear()
{
    return year;
}
int Employee::getSalary()
{
    return salary;
}
string Employee::getAddress()
{
    return address;
}
void Employee::displayData()
{
    cout << getName() << '\t' << getYear() << "\t" << getSalary() << '\t' << getAddress();
}

int main()
{
    Employee e1("Robert", 1994, 500000, "64C - WallsStreet");
    Employee e2("Sam", 2000, 740000, "68D - WallsStreet");
    Employee e3("John", 1999, 600000, "26B - WallsStreet");
    cout << "\nName\tYear\tSalary\tAddress" << '\n';
    e1.displayData();
    cout << '\n';
    e2.displayData();
    cout << '\n';
    e3.displayData();
    cout << '\n';
}

Please do take a look at it and update me accordingly,