Can I restore ios8 on my 6plus?
AAfter updating my 6plus to ios9, I lost all contacts and my siri is not responding. How can I delete the update and restore back to ios8?
iPhone 6 Plus, iOS 9.0.2
You can't.
Try a forced restart: Simultaneously hold down the Home and On buttons until the device shuts down. Ignore the off slider if it appears. Once shut down is complete, if it doesn't restart on it own, turn the device back on using the On button. In some cases it also helps to double click the Home button and close all apps BEFORE doing the restart.
Also, check Settings App > iCloud > make sure Contacts is turned ON