frozen iphone

My brother's iphone is frozen. he was updating it last night and now all it says is "verifying update" on the home screen but you can't open the iphone or restart it. I've tried to hold down the siri button, that with the volume, and I tried to plug it into a computer but it won't connect to any accessories without putting in a passcode, which I cant do. any suggestions on what to do to get it to restart?