Hey Harsha, you can load an extension in chrome browser using ChromOptions in Selenium Webdriver. You can follow these steps to add a chrome extensions to chromeOptions and then load it while running a browser:
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Add "GET CRX" extension from Google Web Store.
 
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Download your extension (in my case its Selenium IDE extension).
 
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Go to Chrome Web Store >> Search for your extension (the one you've already downloaded) >> Click on Get CRX on top-right of the browser >> Click on Get CRX for this Extension. This would download the CRX file.
 
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Now, write your test script by following this code snippet:
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public class openChromeExtension {
    
    public static String driverPath = "C:\\\\Users\\\\Rishabh\\\\Downloads\\\\chromedriver.exe";
    public static void main(String[] args) {
        
        System.setProperty("webdriver.chrome.driver", driverPath);
        ChromeOptions options = new ChromeOptions();
        options.addExtensions(new File("C:\\Users\\Rishabh\\Downloads\\Selenium IDE.crx"));
        DesiredCapabilities capabilities = new DesiredCapabilities();
        capabilities.setCapability(ChromeOptions.CAPABILITY, options);
        ChromeDriver driver = new ChromeDriver(capabilities);
        
        System.out.println("Opening extension");
        driver.get("chrome-extension://mooikfkahbdckldjjndioackbalphokd/index.html");
        driver.navigate().refresh();
        System.out.println("Refresh successfully");
    }
}