1. Is the Apple TV power cord plugged in well to the Apple TV, the surge protector, and is the surge protector plugged in and on?
  2. Is the TV plugged in?
  3. If you don't see it in your list, at the bottom of the list of available Apple TVs, there is an option "Show more" which may list any devices you haven't connected to recently.
  4. Try turning off wifi in the control center (the "beans" in the top right corner next to the date). Wait 15 seconds and turn it back on. Sometimes the list re-populates with that action.