First thing that you need to do is find the ID for the dropdown box you are going to test.
There is a select class used in selenium.
Here is the eg I used to create the above said scenario:
import org.openqa.selenium.support.ui.Select;
System.setProperty("webdriver.chrome.driver","C:\\Yourpath\\chromedriver.exe");
WebDriver driver = new ChromeDriver();
driver.get("https://www.facebook.com");
Select year = new Select(driver.findElement(By.id("date")));
year.selectByVisibleText("27");
Select year = new Select(driver.findElement(By.id("month")));
year.selectByVisibleText("Aug");
Select year = new Select(driver.findElement(By.id("year")));
year.selectByVisibleText("2000");
Thread.sleep(5000);
This is not the legit way but agin this also worked so I am just giving this as an option to do things in a simpler way
System.setProperty("webdriver.chrome.driver","C:\\Yourpath\\chromedriver.exe");
WebDriver driver = new ChromeDriver();
driver.get("https://www.facebook.com");
driver.findElement(By.id("day")).sendKeys("6");
driver.findElement(By.id("month")).sendKeys("Nov");
driver.findElement(By.id("year")).sendKeys("2000");
Thread.wait(5000);
These were the two ways I know to do this.