If you lost the remote for your Apple TV - Apple Support
You can buy a replacement remote that matches the model Apple TV. For Apple TV (3rd generation or earlier) (model 2013 or earlier) [A1218, A1378, A1427, or A1469], users should get the Apple Remote (aluminum) A1294. Apple doesn’t sell these anymore, but select resellers may still have a few.
Replacement remotes will have to be linked to the box: If your Apple TV remote isn’t working - Apple Support (via Wayback Machine) (second half of the page).
Apple TV (2nd generation)
Apple TV (2nd generation) (2010) [A1378] unfortunately isn’t compatible with the software remote in Control Center on iPhone:
“The Apple TV Remote in Control Center works with Apple TV 4K, Apple TV HD, Apple TV (3rd generation), and AirPlay-compatible smart TVs only.” [1]
Identify your Apple TV model - Apple Support
Find your Apple TV model number - Apple Support
Models Apple TV remote and their compatibility - Apple Support
Apple TV (2nd generation) technical specifications - Apple Support