How to deal with parent and child iframes

I have a scenario where I 1st iframe (i.e parent iframe) which has one button on it and clicking on it another iframe gets open (child iframe). I am able to switch to Parent iframe but when I click on the button and tries to interact with Child iframe I’m not able to do it. Can you suggest what should be the better approach to get this type of scenarios working?
Here is my Script:
public class Iframe {

public static void main (String []args) throws InterruptedException {

System.setProperty(“webdriver.chrome.driver”, Constants.Chrome_Driver);

WebDriver driver = new ChromeDriver();

driver.manage().window().maximize();

driver.manage().timeouts().implicitlyWait(30, TimeUnit.SECONDS);

driver.get(“http://automation.cloudaccess.host/administrator”);

driver.findElement(By.id(“mod-login-username”)).sendKeys(“admin”);

driver.findElement(By.id(“mod-login-password”)).sendKeys(“admin@123”);

driver.findElement(By.id(“mod-login-password”)).submit();

driver.findElement(By.linkText(“Components”)).click();

Actions action = new Actions(driver);
action.moveToElement(driver.findElement(By.linkText(“Messaging”))).build().perform();

driver.findElement(By.linkText(“New Private Message”)).click();

driver.findElement(By.className(“wf-editor-header”)).click();

new WebDriverWait(driver, 20).until(ExpectedConditions.elementToBeClickable(By.xpath(“//button[@id=”jform_message_imgmanager”]”))).click();

new WebDriverWait(driver, 20).until(ExpectedConditions.frameToBeAvailableAndSwitchToIt(By.xpath(“//iframe[contains(@src,’&plugin=imgmanager’)]”)));

new WebDriverWait(driver, 20).until(ExpectedConditions.elementToBeClickable(By.xpath(“//*[@id=”browser-actions”]/a[@id=”help”]”))).click();

new WebDriverWait(driver, 20).until(ExpectedConditions.frameToBeAvailableAndSwitchToIt(By.xpath(“//iframe[@id=”mce_inlinepopups_50_ifr”]”)));

new WebDriverWait(driver, 20).until(ExpectedConditions.elementToBeClickable(By.xpath(“//*[@id=”imgmanager.insert”]/i[@class=”icon-file”]”))).click();

driver.quit();

}

}

Error in getting:
Exception in thread “main” org.openqa.selenium.TimeoutException: Expected condition failed: waiting for frame to be available: By.xpath: //iframe[@id=”mce_inlinepopups_50_ifr”] (tried for 20 second(s) with 500 milliseconds interval)
at org.openqa.selenium.support.ui.WebDriverWait.timeoutException(WebDriverWait.java:81)
at org.openqa.selenium.support.ui.FluentWait.until(FluentWait.java:271)
at testScripts.Iframe.main(Iframe.java:53)
Caused by: org.openqa.selenium.NoSuchElementException: Cannot locate an element using By.xpath: //iframe[@id=”mce_inlinepopups_50_ifr”]
For documentation on this error, please visit: http://seleniumhq.org/exceptions/no_such_element.html
Build info: version: ‘3.12.0’, revision: ‘7c6e0b3’, time: ‘2018-05-08T15:15:08.936Z’
System info: host: ‘vowellt4’, ip: ‘127.0.1.1’, os.name: ‘Linux’, os.arch: ‘amd64’, os.version: ‘4.15.0-24-generic’, java.version: ‘1.8.0_171’
Driver info: driver.version: unknown
at org.openqa.selenium.support.ui.ExpectedConditions.lambda$findElement$0(ExpectedConditions.java:896)
at java.util.Optional.orElseThrow(Optional.java:290)
at org.openqa.selenium.support.ui.ExpectedConditions.findElement(ExpectedConditions.java:895)
at org.openqa.selenium.support.ui.ExpectedConditions.access$000(ExpectedConditions.java:44)
at org.openqa.selenium.support.ui.ExpectedConditions$17.apply(ExpectedConditions.java:517)
at org.openqa.selenium.support.ui.ExpectedConditions$17.apply(ExpectedConditions.java:513)
at org.openqa.selenium.support.ui.FluentWait.until(FluentWait.java:248)
… 1 more

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