Use the remote
Press and hold the Select and Play/Pause buttons together for about 5 seconds
Wait for the Firestick to restart
Use the settings menu
Go to Settings
Select My Fire TV
Select Restart
Confirm Restart
Unplug the Firestick
Remove the power cable from the Firestick or wall adapter
Wait 10 seconds
Plug it back in
Restart if frozen
Unplug the Firestick from power
Wait 30 seconds
Plug it back in