Finally got it working for iOS.
System.out.println("swap app test");
//1. Launch the app that you are testing.
//2. Prep for the app to swap (here it's the Photo app) and back to your app.
String PHOTOS_BUNDLE_ID = "com.apple.mobileslideshow"; //this is standard bundle id
// For those using Xcode >=7: select your target and click the *General* tab.
//*Bundle Identifier* is found under *Identity*.
String BUNDLE_ID = "com.example.apple-samplecode.UICatalog"; //
//3. Launch the Photo app.
HashMap args = new HashMap<>();
args.put("bundleId", PHOTOS_BUNDLE_ID);
iosDriver.executeScript("mobile: launchApp", args);
Thread.sleep(1000); //wait for 1000 milll.sec
//4. Swap back to your test app.
args.put("bundleId", BUNDLE_ID);
iosDriver.executeScript("mobile: activateApp", args);
Sources:
https://stackoverflow.com/questions/8873203/how-to-get-bundle-id
https://www.headspin.io/blog/switching-between-ios-apps-during-a-test
I hope you will find it useful.