What do u mean by restart your device ??

1. Restart: Press On/Off button until the Slide to Power Off slider appears, select Slide to Power Off and, after It shuts down, press the On/Off button until the Apple logo appears.
2. Reset: Press the Home and On/Off buttons at the same time and hold them until the Apple logo appears (about 10-15 seconds).
3. Restore: Connect your iPhone to iTunes on your computer, backup, and then select Restore to Factory.

Restart your device means shut it off (hold the on/off button, and then slide the slider when it's presented) - and then start it again (hold the on/off button until you see the Apple logo).

Regarding iMessage and FaceTime, carefully read the article you attached above.

Hi

Apple's instructions for restarting your iPhone are provided here:

Restart your iPhone, iPad, or iPod touch - Apple Support