Try each step then check to see if it is working, move on to the next step only if it still isn't working.
Charge remote for 15-30 minutes.
Remove interference. Try moving anything that could be blocking the signal between the remote and the Apple TV.
Restart Apple TV using a power cable.
Hold TV/Control Center + Volume Down for ~5 seconds.
*If see a disconnected message, then power the remote off/on.
*If you see a connected message it should be working.
Hold Menu or (<) + Left for ~6 seconds.
*If see a disconnected message, then power the remote off/on.
*If you see a connected message it should be working.
Pair the remote Hold Menu or < and up for at least 5 seconds.