I bought an Apple TV 3 gen without a remote how do I use the Apple TV without remote

The Apple TV (3rd generation) needs a functional remote to set up the software Apple TV Remote widget in Control Center on iPhone.

For the Apple TV (3rd generation), your options are:

• buy a replacement Apple Remote (aluminum);
• temporarily borrow an Apple Remote (aluminum) to help set up the software remote;
• restore the Apple TV and connect a wireless keyboard to help set up the software remote;
• restore the Apple TV and connect the CiderTV Mac app to help set up the 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

Apple doesn’t sell the old style Apple Remote (aluminum) (model A1294) for Apple TV (3rd generation or earlier) anymore. Perhaps you can find a third party reseller that still has a few (Amazon, eBay, etc.).