What are the models Apple TV? Identify your Apple TV model - Apple Support
You may need to borrow or buy a functional remote to set the network settings right, so that you can use the iPhone software remote. Set up the Apple TV Remote on your iPhone, iPad, or iPod touch - Apple Support
If you lost the remote for your Apple TV - Apple Support
The Apple TV (4th generation or later) should be straight-forward to pair with, as described, if both devices are already on the same home network.
The Apple TV (3rd generation) needs a functional remote to set up the Apple TV Remote widget in Control Center.
For the Apple TV (3rd generation), your options are:
The Apple TV (2nd generation) is not compatible with the Apple TV Remote widget in Control Center.
For the Apple TV (2nd generation), your option is:
buy a replacement Apple Remote (aluminum).