Steps to Put your iPhone 7 Plus or iPhone 7 in Recovery Mode
1. Connect your iPhone 7 Plus or 7 to the Computer
2. Hold Power and Volume down buttons together for 10 sec. After you see the Apple logo on the screen, keep holding the buttons.
3. Now you will see the iTunes logo and lightning cable on your screen. Your device is now in Recovery mode.
4. Now you can Restore, Update or Downgrade it via iTunes.
How to exit from Recovery Mode if you don't want to Restore it
1. Disconnect your iPhone from the Computer.
2. Hold Volume down and Power button for 15 sec. then release the buttons.
3. Now hold Power to turn on your iPhone as normally.