I cannot see my Apple TV. I have 2 of them and can only see one. Ideas?

Welcome to the Apple Community.

Try the following steps, check whether things are working after each step where appropriate, before trying the next.

1. Check AirPlay is turned on on the Apple TV (turn it off and on if it already is)
2. Check that both devices are on the same network (Settings > Wifi, on the mobile device and Settings > General > Network, on the Apple TV).
3. Restart the Apple TV (Settings > General > Restart).
4. Restart the Apple TV by removing ALL the cables for 30 seconds.
5. Restart your router.
6. Restart your mobile device.

Don't know if this matters or not, try giving both of your Apple TVs different names (i.e., they aren't both named "Apple TV"). That way, at least, you'd be able to tell at-a-glance whether or not you could actually see both.